diff --git a/tests/base.py b/tests/base.py
index e688abd..64f6657 100755
--- a/tests/base.py
+++ b/tests/base.py
@@ -641,6 +641,7 @@
         self.is_merged = False
         self.merge_message = None
         self.state = 'open'
+        self.url = 'https://%s/%s/pull/%s' % (github.server, project, number)
         self._createPRRef()
         self._addCommitToRepo(files=files)
         self._updateTimeStamp()
diff --git a/tests/fixtures/config/cross-source/git/common-config/playbooks/nonvoting-project-merge.yaml b/tests/fixtures/config/cross-source/git/common-config/playbooks/nonvoting-project-merge.yaml
new file mode 100644
index 0000000..f679dce
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/common-config/playbooks/nonvoting-project-merge.yaml
@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []
diff --git a/tests/fixtures/config/cross-source/git/common-config/playbooks/nonvoting-project-test1.yaml b/tests/fixtures/config/cross-source/git/common-config/playbooks/nonvoting-project-test1.yaml
new file mode 100644
index 0000000..f679dce
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/common-config/playbooks/nonvoting-project-test1.yaml
@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []
diff --git a/tests/fixtures/config/cross-source/git/common-config/playbooks/nonvoting-project-test2.yaml b/tests/fixtures/config/cross-source/git/common-config/playbooks/nonvoting-project-test2.yaml
new file mode 100644
index 0000000..f679dce
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/common-config/playbooks/nonvoting-project-test2.yaml
@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []
diff --git a/tests/fixtures/config/cross-source/git/common-config/playbooks/project-merge.yaml b/tests/fixtures/config/cross-source/git/common-config/playbooks/project-merge.yaml
new file mode 100644
index 0000000..f679dce
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/common-config/playbooks/project-merge.yaml
@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []
diff --git a/tests/fixtures/config/cross-source/git/common-config/playbooks/project-post.yaml b/tests/fixtures/config/cross-source/git/common-config/playbooks/project-post.yaml
new file mode 100644
index 0000000..f679dce
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/common-config/playbooks/project-post.yaml
@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []
diff --git a/tests/fixtures/config/cross-source/git/common-config/playbooks/project-test1.yaml b/tests/fixtures/config/cross-source/git/common-config/playbooks/project-test1.yaml
new file mode 100644
index 0000000..f679dce
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/common-config/playbooks/project-test1.yaml
@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []
diff --git a/tests/fixtures/config/cross-source/git/common-config/playbooks/project-test2.yaml b/tests/fixtures/config/cross-source/git/common-config/playbooks/project-test2.yaml
new file mode 100644
index 0000000..f679dce
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/common-config/playbooks/project-test2.yaml
@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []
diff --git a/tests/fixtures/config/cross-source/git/common-config/playbooks/project-testfile.yaml b/tests/fixtures/config/cross-source/git/common-config/playbooks/project-testfile.yaml
new file mode 100644
index 0000000..f679dce
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/common-config/playbooks/project-testfile.yaml
@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []
diff --git a/tests/fixtures/config/cross-source/git/common-config/playbooks/project1-project2-integration.yaml b/tests/fixtures/config/cross-source/git/common-config/playbooks/project1-project2-integration.yaml
new file mode 100644
index 0000000..f679dce
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/common-config/playbooks/project1-project2-integration.yaml
@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []
diff --git a/tests/fixtures/config/cross-source/git/common-config/zuul.yaml b/tests/fixtures/config/cross-source/git/common-config/zuul.yaml
new file mode 100644
index 0000000..abdc34a
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/common-config/zuul.yaml
@@ -0,0 +1,168 @@
+- pipeline:
+    name: check
+    manager: independent
+    trigger:
+      gerrit:
+        - event: patchset-created
+      github:
+        - event: pull_request
+          action: edited
+    success:
+      gerrit:
+        Verified: 1
+      github: {}
+    failure:
+      gerrit:
+        Verified: -1
+      github: {}
+
+- pipeline:
+    name: gate
+    manager: dependent
+    success-message: Build succeeded (gate).
+    require:
+      github:
+        label: approved
+      gerrit:
+        approval:
+          - Approved: 1
+    trigger:
+      gerrit:
+        - event: comment-added
+          approval:
+            - Approved: 1
+      github:
+        - event: pull_request
+          action: edited
+        - event: pull_request
+          action: labeled
+          label: approved
+    success:
+      gerrit:
+        Verified: 2
+        submit: true
+      github:
+        merge: true
+    failure:
+      gerrit:
+        Verified: -2
+      github: {}
+    start:
+      gerrit:
+        Verified: 0
+      github: {}
+    precedence: high
+
+- pipeline:
+    name: post
+    manager: independent
+    trigger:
+      gerrit:
+        - event: ref-updated
+          ref: ^(?!refs/).*$
+    precedence: low
+
+- job:
+    name: base
+    parent: null
+
+- job:
+    name: project-merge
+    hold-following-changes: true
+    nodeset:
+      nodes:
+        - name: controller
+          label: label1
+    run: playbooks/project-merge.yaml
+
+- job:
+    name: project-test1
+    attempts: 4
+    nodeset:
+      nodes:
+        - name: controller
+          label: label1
+    run: playbooks/project-test1.yaml
+
+- job:
+    name: project-test1
+    branches: stable
+    nodeset:
+      nodes:
+        - name: controller
+          label: label2
+    run: playbooks/project-test1.yaml
+
+- job:
+    name: project-post
+    nodeset:
+      nodes:
+        - name: static
+          label: ubuntu-xenial
+    run: playbooks/project-post.yaml
+
+- job:
+    name: project-test2
+    nodeset:
+      nodes:
+        - name: controller
+          label: label1
+    run: playbooks/project-test2.yaml
+
+- job:
+    name: project1-project2-integration
+    nodeset:
+      nodes:
+        - name: controller
+          label: label1
+    run: playbooks/project1-project2-integration.yaml
+
+- job:
+    name: project-testfile
+    files:
+      - .*-requires
+    run: playbooks/project-testfile.yaml
+
+- project:
+    name: gerrit/project1
+    check:
+      jobs:
+        - project-merge
+        - project-test1:
+            dependencies: project-merge
+        - project-test2:
+            dependencies: project-merge
+        - project1-project2-integration:
+            dependencies: project-merge
+    gate:
+      queue: integrated
+      jobs:
+        - project-merge
+        - project-test1:
+            dependencies: project-merge
+        - project-test2:
+            dependencies: project-merge
+        - project1-project2-integration:
+            dependencies: project-merge
+
+- project:
+    name: github/project2
+    check:
+      jobs:
+        - project-merge
+        - project-test1:
+            dependencies: project-merge
+        - project-test2:
+            dependencies: project-merge
+        - project1-project2-integration:
+            dependencies: project-merge
+    gate:
+      queue: integrated
+      jobs:
+        - project-merge
+        - project-test1:
+            dependencies: project-merge
+        - project-test2:
+            dependencies: project-merge
+        - project1-project2-integration:
+            dependencies: project-merge
diff --git a/tests/fixtures/config/cross-source/git/gerrit_project1/README b/tests/fixtures/config/cross-source/git/gerrit_project1/README
new file mode 100644
index 0000000..9daeafb
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/gerrit_project1/README
@@ -0,0 +1 @@
+test
diff --git a/tests/fixtures/config/cross-source/git/github_project2/README b/tests/fixtures/config/cross-source/git/github_project2/README
new file mode 100644
index 0000000..9daeafb
--- /dev/null
+++ b/tests/fixtures/config/cross-source/git/github_project2/README
@@ -0,0 +1 @@
+test
diff --git a/tests/fixtures/config/cross-source/main.yaml b/tests/fixtures/config/cross-source/main.yaml
new file mode 100644
index 0000000..bf85c33
--- /dev/null
+++ b/tests/fixtures/config/cross-source/main.yaml
@@ -0,0 +1,11 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-projects:
+          - common-config
+        untrusted-projects:
+          - gerrit/project1
+      github:
+        untrusted-projects:
+          - github/project2
diff --git a/tests/fixtures/zuul-gerrit-github.conf b/tests/fixtures/zuul-gerrit-github.conf
new file mode 100644
index 0000000..d3cbf7b
--- /dev/null
+++ b/tests/fixtures/zuul-gerrit-github.conf
@@ -0,0 +1,35 @@
+[gearman]
+server=127.0.0.1
+
+[statsd]
+# note, use 127.0.0.1 rather than localhost to avoid getting ipv6
+# see: https://github.com/jsocol/pystatsd/issues/61
+server=127.0.0.1
+
+[scheduler]
+tenant_config=main.yaml
+
+[merger]
+git_dir=/tmp/zuul-test/merger-git
+git_user_email=zuul@example.com
+git_user_name=zuul
+
+[executor]
+git_dir=/tmp/zuul-test/executor-git
+
+[connection gerrit]
+driver=gerrit
+server=review.example.com
+user=jenkins
+sshkey=fake_id_rsa_path
+
+[connection github]
+driver=github
+webhook_token=0000000000000000000000000000000000000000
+
+[connection smtp]
+driver=smtp
+server=localhost
+port=25
+default_from=zuul@example.com
+default_to=you@example.com
diff --git a/tests/unit/test_cross_crd.py b/tests/unit/test_cross_crd.py
new file mode 100644
index 0000000..7d68989
--- /dev/null
+++ b/tests/unit/test_cross_crd.py
@@ -0,0 +1,950 @@
+#!/usr/bin/env python
+
+# Copyright 2012 Hewlett-Packard Development Company, L.P.
+# Copyright 2018 Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+from tests.base import (
+    ZuulTestCase,
+)
+
+
+class TestGerritToGithubCRD(ZuulTestCase):
+    config_file = 'zuul-gerrit-github.conf'
+    tenant_config_file = 'config/cross-source/main.yaml'
+
+    def test_crd_gate(self):
+        "Test cross-repo dependencies"
+        A = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'A')
+        B = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'B')
+
+        A.addApproval('Code-Review', 2)
+
+        AM2 = self.fake_gerrit.addFakeChange('gerrit/project1', 'master',
+                                             'AM2')
+        AM1 = self.fake_gerrit.addFakeChange('gerrit/project1', 'master',
+                                             'AM1')
+        AM2.setMerged()
+        AM1.setMerged()
+
+        # A -> AM1 -> AM2
+        # A Depends-On: B
+        # M2 is here to make sure it is never queried.  If it is, it
+        # means zuul is walking down the entire history of merged
+        # changes.
+
+        A.setDependsOn(AM1, 1)
+        AM1.setDependsOn(AM2, 1)
+
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.url)
+
+        self.fake_gerrit.addEvent(A.addApproval('Approved', 1))
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'NEW')
+        self.assertFalse(B.is_merged)
+
+        for connection in self.connections.connections.values():
+            connection.maintainCache([])
+
+        self.executor_server.hold_jobs_in_build = True
+        B.addLabel('approved')
+        self.fake_gerrit.addEvent(A.addApproval('Approved', 1))
+        self.waitUntilSettled()
+
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+        self.assertEqual(AM2.queried, 0)
+        self.assertEqual(A.data['status'], 'MERGED')
+        self.assertTrue(B.is_merged)
+        self.assertEqual(A.reported, 2)
+        self.assertEqual(len(B.comments), 2)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'gerrit/project1').changes
+        self.assertEqual(changes, '1,%s 1,1' % B.head_sha)
+
+    def test_crd_branch(self):
+        "Test cross-repo dependencies in multiple branches"
+
+        self.create_branch('github/project2', 'mp')
+        A = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'A')
+        B = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'B')
+        C1 = self.fake_github.openFakePullRequest('github/project2', 'mp',
+                                                  'C1')
+
+        A.addApproval('Code-Review', 2)
+
+        # A Depends-On: B+C1
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\nDepends-On: %s\n' % (
+            A.subject, B.url, C1.url)
+
+        self.executor_server.hold_jobs_in_build = True
+        B.addLabel('approved')
+        C1.addLabel('approved')
+        self.fake_gerrit.addEvent(A.addApproval('Approved', 1))
+        self.waitUntilSettled()
+
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'MERGED')
+        self.assertTrue(B.is_merged)
+        self.assertTrue(C1.is_merged)
+        self.assertEqual(A.reported, 2)
+        self.assertEqual(len(B.comments), 2)
+        self.assertEqual(len(C1.comments), 2)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'gerrit/project1').changes
+        self.assertEqual(changes, '1,%s 2,%s 1,1' %
+                         (B.head_sha, C1.head_sha))
+
+    def test_crd_gate_reverse(self):
+        "Test reverse cross-repo dependencies"
+        A = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'A')
+        B = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'B')
+        A.addApproval('Code-Review', 2)
+
+        # A Depends-On: B
+
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.url)
+
+        self.fake_gerrit.addEvent(A.addApproval('Approved', 1))
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'NEW')
+        self.assertFalse(B.is_merged)
+
+        self.executor_server.hold_jobs_in_build = True
+        A.addApproval('Approved', 1)
+        self.fake_github.emitEvent(B.addLabel('approved'))
+        self.waitUntilSettled()
+
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'MERGED')
+        self.assertTrue(B.is_merged)
+        self.assertEqual(A.reported, 2)
+        self.assertEqual(len(B.comments), 2)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'gerrit/project1').changes
+        self.assertEqual(changes, '1,%s 1,1' %
+                         (B.head_sha,))
+
+    def test_crd_cycle(self):
+        "Test cross-repo dependency cycles"
+        A = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'A')
+        msg = "Depends-On: %s" % (A.data['url'],)
+        B = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'B', body=msg)
+        A.addApproval('Code-Review', 2)
+        B.addLabel('approved')
+
+        # A -> B -> A (via commit-depends)
+
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.url)
+
+        self.fake_gerrit.addEvent(A.addApproval('Approved', 1))
+        self.waitUntilSettled()
+
+        self.assertEqual(A.reported, 0)
+        self.assertEqual(len(B.comments), 0)
+        self.assertEqual(A.data['status'], 'NEW')
+        self.assertFalse(B.is_merged)
+
+    def test_crd_gate_unknown(self):
+        "Test unknown projects in dependent pipeline"
+        self.init_repo("github/unknown", tag='init')
+        A = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'A')
+        B = self.fake_github.openFakePullRequest('github/unknown', 'master',
+                                                 'B')
+        A.addApproval('Code-Review', 2)
+
+        # A Depends-On: B
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.url)
+
+        event = B.addLabel('approved')
+        self.fake_gerrit.addEvent(A.addApproval('Approved', 1))
+        self.waitUntilSettled()
+
+        # Unknown projects cannot share a queue with any other
+        # since they don't have common jobs with any other (they have no jobs).
+        # Changes which depend on unknown project changes
+        # should not be processed in dependent pipeline
+        self.assertEqual(A.data['status'], 'NEW')
+        self.assertFalse(B.is_merged)
+        self.assertEqual(A.reported, 0)
+        self.assertEqual(len(B.comments), 0)
+        self.assertEqual(len(self.history), 0)
+
+        # Simulate change B being gated outside this layout Set the
+        # change merged before submitting the event so that when the
+        # event triggers a gerrit query to update the change, we get
+        # the information that it was merged.
+        B.setMerged('merged')
+        self.fake_github.emitEvent(event)
+        self.waitUntilSettled()
+        self.assertEqual(len(self.history), 0)
+
+        # Now that B is merged, A should be able to be enqueued and
+        # merged.
+        self.fake_gerrit.addEvent(A.addApproval('Approved', 1))
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'MERGED')
+        self.assertEqual(A.reported, 2)
+        self.assertTrue(B.is_merged)
+        self.assertEqual(len(B.comments), 0)
+
+    def test_crd_check(self):
+        "Test cross-repo dependencies in independent pipelines"
+        self.executor_server.hold_jobs_in_build = True
+        self.gearman_server.hold_jobs_in_queue = True
+        A = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'A')
+        B = self.fake_github.openFakePullRequest(
+            'github/project2', 'master', 'B')
+
+        # A Depends-On: B
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.url)
+
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+
+        self.gearman_server.hold_jobs_in_queue = False
+        self.gearman_server.release()
+        self.waitUntilSettled()
+
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+
+        self.assertTrue(self.builds[0].hasChanges(A, B))
+
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'NEW')
+        self.assertFalse(B.is_merged)
+        self.assertEqual(A.reported, 1)
+        self.assertEqual(len(B.comments), 0)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'gerrit/project1').changes
+        self.assertEqual(changes, '1,%s 1,1' %
+                         (B.head_sha,))
+
+        tenant = self.sched.abide.tenants.get('tenant-one')
+        self.assertEqual(len(tenant.layout.pipelines['check'].queues), 0)
+
+    def test_crd_check_duplicate(self):
+        "Test duplicate check in independent pipelines"
+        self.executor_server.hold_jobs_in_build = True
+        A = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'A')
+        B = self.fake_github.openFakePullRequest(
+            'github/project2', 'master', 'B')
+
+        # A Depends-On: B
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.url)
+        tenant = self.sched.abide.tenants.get('tenant-one')
+        check_pipeline = tenant.layout.pipelines['check']
+
+        # Add two dependent changes...
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.assertEqual(len(check_pipeline.getAllItems()), 2)
+
+        # ...make sure the live one is not duplicated...
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.assertEqual(len(check_pipeline.getAllItems()), 2)
+
+        # ...but the non-live one is able to be.
+        self.fake_github.emitEvent(B.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+        self.assertEqual(len(check_pipeline.getAllItems()), 3)
+
+        # Release jobs in order to avoid races with change A jobs
+        # finishing before change B jobs.
+        self.orderedRelease()
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'NEW')
+        self.assertFalse(B.is_merged)
+        self.assertEqual(A.reported, 1)
+        self.assertEqual(len(B.comments), 1)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'gerrit/project1').changes
+        self.assertEqual(changes, '1,%s 1,1' %
+                         (B.head_sha,))
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'github/project2').changes
+        self.assertEqual(changes, '1,%s' %
+                         (B.head_sha,))
+        self.assertEqual(len(tenant.layout.pipelines['check'].queues), 0)
+
+        self.assertIn('Build succeeded', A.messages[0])
+
+    def _test_crd_check_reconfiguration(self, project1, project2):
+        "Test cross-repo dependencies re-enqueued in independent pipelines"
+
+        self.gearman_server.hold_jobs_in_queue = True
+        A = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'A')
+        B = self.fake_github.openFakePullRequest(
+            'github/project2', 'master', 'B')
+
+        # A Depends-On: B
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.url)
+
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+
+        self.sched.reconfigure(self.config)
+
+        # Make sure the items still share a change queue, and the
+        # first one is not live.
+        tenant = self.sched.abide.tenants.get('tenant-one')
+        self.assertEqual(len(tenant.layout.pipelines['check'].queues), 1)
+        queue = tenant.layout.pipelines['check'].queues[0]
+        first_item = queue.queue[0]
+        for item in queue.queue:
+            self.assertEqual(item.queue, first_item.queue)
+        self.assertFalse(first_item.live)
+        self.assertTrue(queue.queue[1].live)
+
+        self.gearman_server.hold_jobs_in_queue = False
+        self.gearman_server.release()
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'NEW')
+        self.assertFalse(B.is_merged)
+        self.assertEqual(A.reported, 1)
+        self.assertEqual(len(B.comments), 0)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'gerrit/project1').changes
+        self.assertEqual(changes, '1,%s 1,1' %
+                         (B.head_sha,))
+        self.assertEqual(len(tenant.layout.pipelines['check'].queues), 0)
+
+    def test_crd_check_reconfiguration(self):
+        self._test_crd_check_reconfiguration('org/project1', 'org/project2')
+
+    def test_crd_undefined_project(self):
+        """Test that undefined projects in dependencies are handled for
+        independent pipelines"""
+        # It's a hack for fake github,
+        # as it implies repo creation upon the creation of any change
+        self.init_repo("github/unknown", tag='init')
+        self._test_crd_check_reconfiguration('gerrit/project1',
+                                             'github/unknown')
+
+    def test_crd_check_transitive(self):
+        "Test transitive cross-repo dependencies"
+        # Specifically, if A -> B -> C, and C gets a new patchset and
+        # A gets a new patchset, ensure the test of A,2 includes B,1
+        # and C,2 (not C,1 which would indicate stale data in the
+        # cache for B).
+        A = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'A')
+        C = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'C')
+        # B Depends-On: C
+        msg = "Depends-On: %s" % (C.data['url'],)
+        B = self.fake_github.openFakePullRequest(
+            'github/project2', 'master', 'B', body=msg)
+
+        # A Depends-On: B
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.url)
+
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.assertEqual(self.history[-1].changes, '2,1 1,%s 1,1' %
+                         (B.head_sha,))
+
+        self.fake_github.emitEvent(B.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+        self.assertEqual(self.history[-1].changes, '2,1 1,%s' %
+                         (B.head_sha,))
+
+        self.fake_gerrit.addEvent(C.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.assertEqual(self.history[-1].changes, '2,1')
+
+        C.addPatchset()
+        self.fake_gerrit.addEvent(C.getPatchsetCreatedEvent(2))
+        self.waitUntilSettled()
+        self.assertEqual(self.history[-1].changes, '2,2')
+
+        A.addPatchset()
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(2))
+        self.waitUntilSettled()
+        self.assertEqual(self.history[-1].changes, '2,2 1,%s 1,2' %
+                         (B.head_sha,))
+
+    def test_crd_check_unknown(self):
+        "Test unknown projects in independent pipeline"
+        self.init_repo("github/unknown", tag='init')
+        A = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'A')
+        B = self.fake_github.openFakePullRequest(
+            'github/unknown', 'master', 'B')
+        # A Depends-On: B
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.url)
+
+        # Make sure zuul has seen an event on B.
+        self.fake_github.emitEvent(B.getPullRequestEditedEvent())
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'NEW')
+        self.assertEqual(A.reported, 1)
+        self.assertFalse(B.is_merged)
+        self.assertEqual(len(B.comments), 0)
+
+    def test_crd_cycle_join(self):
+        "Test an updated change creates a cycle"
+        A = self.fake_github.openFakePullRequest(
+            'github/project2', 'master', 'A')
+
+        self.fake_github.emitEvent(A.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+        self.assertEqual(len(A.comments), 1)
+
+        # Create B->A
+        B = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'B')
+        B.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            B.subject, A.url)
+        self.fake_gerrit.addEvent(B.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+
+        # Dep is there so zuul should have reported on B
+        self.assertEqual(B.reported, 1)
+
+        # Update A to add A->B (a cycle).
+        A.editBody('Depends-On: %s\n' % (B.data['url']))
+        self.fake_github.emitEvent(A.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+
+        # Dependency cycle injected so zuul should not have reported again on A
+        self.assertEqual(len(A.comments), 1)
+
+        # Now if we update B to remove the depends-on, everything
+        # should be okay.  B; A->B
+
+        B.addPatchset()
+        B.data['commitMessage'] = '%s\n' % (B.subject,)
+        self.fake_github.emitEvent(A.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+
+        # Cycle was removed so now zuul should have reported again on A
+        self.assertEqual(len(A.comments), 2)
+
+        self.fake_gerrit.addEvent(B.getPatchsetCreatedEvent(2))
+        self.waitUntilSettled()
+        self.assertEqual(B.reported, 2)
+
+
+class TestGithubToGerritCRD(ZuulTestCase):
+    config_file = 'zuul-gerrit-github.conf'
+    tenant_config_file = 'config/cross-source/main.yaml'
+
+    def test_crd_gate(self):
+        "Test cross-repo dependencies"
+        A = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'A')
+        B = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'B')
+
+        B.addApproval('Code-Review', 2)
+
+        # A Depends-On: B
+        A.editBody('Depends-On: %s\n' % (B.data['url']))
+
+        event = A.addLabel('approved')
+        self.fake_github.emitEvent(event)
+        self.waitUntilSettled()
+
+        self.assertFalse(A.is_merged)
+        self.assertEqual(B.data['status'], 'NEW')
+
+        for connection in self.connections.connections.values():
+            connection.maintainCache([])
+
+        self.executor_server.hold_jobs_in_build = True
+        B.addApproval('Approved', 1)
+        self.fake_github.emitEvent(event)
+        self.waitUntilSettled()
+
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+        self.assertTrue(A.is_merged)
+        self.assertEqual(B.data['status'], 'MERGED')
+        self.assertEqual(len(A.comments), 2)
+        self.assertEqual(B.reported, 2)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'github/project2').changes
+        self.assertEqual(changes, '1,1 1,%s' % A.head_sha)
+
+    def test_crd_branch(self):
+        "Test cross-repo dependencies in multiple branches"
+
+        self.create_branch('gerrit/project1', 'mp')
+        A = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'A')
+        B = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'B')
+        C1 = self.fake_gerrit.addFakeChange('gerrit/project1', 'mp', 'C1')
+
+        B.addApproval('Code-Review', 2)
+        C1.addApproval('Code-Review', 2)
+
+        # A Depends-On: B+C1
+        A.editBody('Depends-On: %s\nDepends-On: %s\n' % (
+            B.data['url'], C1.data['url']))
+
+        self.executor_server.hold_jobs_in_build = True
+        B.addApproval('Approved', 1)
+        C1.addApproval('Approved', 1)
+        self.fake_github.emitEvent(A.addLabel('approved'))
+        self.waitUntilSettled()
+
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+        self.assertTrue(A.is_merged)
+        self.assertEqual(B.data['status'], 'MERGED')
+        self.assertEqual(C1.data['status'], 'MERGED')
+        self.assertEqual(len(A.comments), 2)
+        self.assertEqual(B.reported, 2)
+        self.assertEqual(C1.reported, 2)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'github/project2').changes
+        self.assertEqual(changes, '1,1 2,1 1,%s' %
+                         (A.head_sha,))
+
+    def test_crd_gate_reverse(self):
+        "Test reverse cross-repo dependencies"
+        A = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'A')
+        B = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'B')
+        B.addApproval('Code-Review', 2)
+
+        # A Depends-On: B
+        A.editBody('Depends-On: %s\n' % (B.data['url'],))
+
+        self.fake_github.emitEvent(A.addLabel('approved'))
+        self.waitUntilSettled()
+
+        self.assertFalse(A.is_merged)
+        self.assertEqual(B.data['status'], 'NEW')
+
+        self.executor_server.hold_jobs_in_build = True
+        A.addLabel('approved')
+        self.fake_gerrit.addEvent(B.addApproval('Approved', 1))
+        self.waitUntilSettled()
+
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+        self.assertTrue(A.is_merged)
+        self.assertEqual(B.data['status'], 'MERGED')
+        self.assertEqual(len(A.comments), 2)
+        self.assertEqual(B.reported, 2)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'github/project2').changes
+        self.assertEqual(changes, '1,1 1,%s' %
+                         (A.head_sha,))
+
+    def test_crd_cycle(self):
+        "Test cross-repo dependency cycles"
+        A = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'A')
+        B = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'B')
+        B.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            B.subject, A.url)
+
+        B.addApproval('Code-Review', 2)
+        B.addApproval('Approved', 1)
+
+        # A -> B -> A (via commit-depends)
+        A.editBody('Depends-On: %s\n' % (B.data['url'],))
+
+        self.fake_github.emitEvent(A.addLabel('approved'))
+        self.waitUntilSettled()
+
+        self.assertEqual(len(A.comments), 0)
+        self.assertEqual(B.reported, 0)
+        self.assertFalse(A.is_merged)
+        self.assertEqual(B.data['status'], 'NEW')
+
+    def test_crd_gate_unknown(self):
+        "Test unknown projects in dependent pipeline"
+        self.init_repo("gerrit/unknown", tag='init')
+        A = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'A')
+        B = self.fake_gerrit.addFakeChange('gerrit/unknown', 'master', 'B')
+        B.addApproval('Code-Review', 2)
+
+        # A Depends-On: B
+        A.editBody('Depends-On: %s\n' % (B.data['url'],))
+
+        B.addApproval('Approved', 1)
+        event = A.addLabel('approved')
+        self.fake_github.emitEvent(event)
+        self.waitUntilSettled()
+
+        # Unknown projects cannot share a queue with any other
+        # since they don't have common jobs with any other (they have no jobs).
+        # Changes which depend on unknown project changes
+        # should not be processed in dependent pipeline
+        self.assertFalse(A.is_merged)
+        self.assertEqual(B.data['status'], 'NEW')
+        self.assertEqual(len(A.comments), 0)
+        self.assertEqual(B.reported, 0)
+        self.assertEqual(len(self.history), 0)
+
+        # Simulate change B being gated outside this layout Set the
+        # change merged before submitting the event so that when the
+        # event triggers a gerrit query to update the change, we get
+        # the information that it was merged.
+        B.setMerged()
+        self.fake_gerrit.addEvent(B.addApproval('Approved', 1))
+        self.waitUntilSettled()
+        self.assertEqual(len(self.history), 0)
+
+        # Now that B is merged, A should be able to be enqueued and
+        # merged.
+        self.fake_github.emitEvent(event)
+        self.waitUntilSettled()
+
+        self.assertTrue(A.is_merged)
+        self.assertEqual(len(A.comments), 2)
+        self.assertEqual(B.data['status'], 'MERGED')
+        self.assertEqual(B.reported, 0)
+
+    def test_crd_check(self):
+        "Test cross-repo dependencies in independent pipelines"
+        self.executor_server.hold_jobs_in_build = True
+        self.gearman_server.hold_jobs_in_queue = True
+        A = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'A')
+        B = self.fake_gerrit.addFakeChange(
+            'gerrit/project1', 'master', 'B')
+
+        # A Depends-On: B
+        A.editBody('Depends-On: %s\n' % (B.data['url'],))
+
+        self.fake_github.emitEvent(A.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+
+        self.gearman_server.hold_jobs_in_queue = False
+        self.gearman_server.release()
+        self.waitUntilSettled()
+
+        self.executor_server.release('.*-merge')
+        self.waitUntilSettled()
+
+        self.assertTrue(self.builds[0].hasChanges(A, B))
+
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+        self.assertFalse(A.is_merged)
+        self.assertEqual(B.data['status'], 'NEW')
+        self.assertEqual(len(A.comments), 1)
+        self.assertEqual(B.reported, 0)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'github/project2').changes
+        self.assertEqual(changes, '1,1 1,%s' %
+                         (A.head_sha,))
+
+        tenant = self.sched.abide.tenants.get('tenant-one')
+        self.assertEqual(len(tenant.layout.pipelines['check'].queues), 0)
+
+    def test_crd_check_duplicate(self):
+        "Test duplicate check in independent pipelines"
+        self.executor_server.hold_jobs_in_build = True
+        A = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'A')
+        B = self.fake_gerrit.addFakeChange(
+            'gerrit/project1', 'master', 'B')
+
+        # A Depends-On: B
+        A.editBody('Depends-On: %s\n' % (B.data['url'],))
+        tenant = self.sched.abide.tenants.get('tenant-one')
+        check_pipeline = tenant.layout.pipelines['check']
+
+        # Add two dependent changes...
+        self.fake_github.emitEvent(A.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+        self.assertEqual(len(check_pipeline.getAllItems()), 2)
+
+        # ...make sure the live one is not duplicated...
+        self.fake_github.emitEvent(A.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+        self.assertEqual(len(check_pipeline.getAllItems()), 2)
+
+        # ...but the non-live one is able to be.
+        self.fake_gerrit.addEvent(B.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.assertEqual(len(check_pipeline.getAllItems()), 3)
+
+        # Release jobs in order to avoid races with change A jobs
+        # finishing before change B jobs.
+        self.orderedRelease()
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+        self.assertFalse(A.is_merged)
+        self.assertEqual(B.data['status'], 'NEW')
+        self.assertEqual(len(A.comments), 1)
+        self.assertEqual(B.reported, 1)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'github/project2').changes
+        self.assertEqual(changes, '1,1 1,%s' %
+                         (A.head_sha,))
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'gerrit/project1').changes
+        self.assertEqual(changes, '1,1')
+        self.assertEqual(len(tenant.layout.pipelines['check'].queues), 0)
+
+        self.assertIn('Build succeeded', A.comments[0])
+
+    def _test_crd_check_reconfiguration(self, project1, project2):
+        "Test cross-repo dependencies re-enqueued in independent pipelines"
+
+        self.gearman_server.hold_jobs_in_queue = True
+        A = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'A')
+        B = self.fake_gerrit.addFakeChange(
+            'gerrit/project1', 'master', 'B')
+
+        # A Depends-On: B
+        A.editBody('Depends-On: %s\n' % (B.data['url'],))
+
+        self.fake_github.emitEvent(A.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+
+        self.sched.reconfigure(self.config)
+
+        # Make sure the items still share a change queue, and the
+        # first one is not live.
+        tenant = self.sched.abide.tenants.get('tenant-one')
+        self.assertEqual(len(tenant.layout.pipelines['check'].queues), 1)
+        queue = tenant.layout.pipelines['check'].queues[0]
+        first_item = queue.queue[0]
+        for item in queue.queue:
+            self.assertEqual(item.queue, first_item.queue)
+        self.assertFalse(first_item.live)
+        self.assertTrue(queue.queue[1].live)
+
+        self.gearman_server.hold_jobs_in_queue = False
+        self.gearman_server.release()
+        self.waitUntilSettled()
+
+        self.assertFalse(A.is_merged)
+        self.assertEqual(B.data['status'], 'NEW')
+        self.assertEqual(len(A.comments), 1)
+        self.assertEqual(B.reported, 0)
+
+        changes = self.getJobFromHistory(
+            'project-merge', 'github/project2').changes
+        self.assertEqual(changes, '1,1 1,%s' %
+                         (A.head_sha,))
+        self.assertEqual(len(tenant.layout.pipelines['check'].queues), 0)
+
+    def test_crd_check_reconfiguration(self):
+        self._test_crd_check_reconfiguration('org/project1', 'org/project2')
+
+    def test_crd_undefined_project(self):
+        """Test that undefined projects in dependencies are handled for
+        independent pipelines"""
+        # It's a hack for fake gerrit,
+        # as it implies repo creation upon the creation of any change
+        self.init_repo("gerrit/unknown", tag='init')
+        self._test_crd_check_reconfiguration('github/project2',
+                                             'gerrit/unknown')
+
+    def test_crd_check_transitive(self):
+        "Test transitive cross-repo dependencies"
+        # Specifically, if A -> B -> C, and C gets a new patchset and
+        # A gets a new patchset, ensure the test of A,2 includes B,1
+        # and C,2 (not C,1 which would indicate stale data in the
+        # cache for B).
+        A = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'A')
+        B = self.fake_gerrit.addFakeChange('gerrit/project1', 'master', 'B')
+        C = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'C')
+
+        # B Depends-On: C
+        B.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            B.subject, C.url)
+
+        # A Depends-On: B
+        A.editBody('Depends-On: %s\n' % (B.data['url'],))
+
+        self.fake_github.emitEvent(A.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+        self.assertEqual(self.history[-1].changes, '2,%s 1,1 1,%s' %
+                         (C.head_sha, A.head_sha))
+
+        self.fake_gerrit.addEvent(B.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.assertEqual(self.history[-1].changes, '2,%s 1,1' %
+                         (C.head_sha,))
+
+        self.fake_github.emitEvent(C.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+        self.assertEqual(self.history[-1].changes, '2,%s' %
+                         (C.head_sha,))
+
+        new_c_head = C.head_sha
+        C.addCommit()
+        old_c_head = C.head_sha
+        self.assertNotEqual(old_c_head, new_c_head)
+        self.fake_github.emitEvent(C.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+        self.assertEqual(self.history[-1].changes, '2,%s' %
+                         (C.head_sha,))
+
+        new_a_head = A.head_sha
+        A.addCommit()
+        old_a_head = A.head_sha
+        self.assertNotEqual(old_a_head, new_a_head)
+        self.fake_github.emitEvent(A.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+        self.assertEqual(self.history[-1].changes, '2,%s 1,1 1,%s' %
+                         (C.head_sha, A.head_sha,))
+
+    def test_crd_check_unknown(self):
+        "Test unknown projects in independent pipeline"
+        self.init_repo("gerrit/unknown", tag='init')
+        A = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'A')
+        B = self.fake_gerrit.addFakeChange(
+            'gerrit/unknown', 'master', 'B')
+
+        # A Depends-On: B
+        A.editBody('Depends-On: %s\n' % (B.data['url'],))
+
+        # Make sure zuul has seen an event on B.
+        self.fake_gerrit.addEvent(B.getPatchsetCreatedEvent(1))
+        self.fake_github.emitEvent(A.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+
+        self.assertFalse(A.is_merged)
+        self.assertEqual(len(A.comments), 1)
+        self.assertEqual(B.data['status'], 'NEW')
+        self.assertEqual(B.reported, 0)
+
+    def test_crd_cycle_join(self):
+        "Test an updated change creates a cycle"
+        A = self.fake_gerrit.addFakeChange(
+            'gerrit/project1', 'master', 'A')
+
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.assertEqual(A.reported, 1)
+
+        # Create B->A
+        B = self.fake_github.openFakePullRequest('github/project2', 'master',
+                                                 'B')
+        B.editBody('Depends-On: %s\n' % (A.data['url'],))
+        self.fake_github.emitEvent(B.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+
+        # Dep is there so zuul should have reported on B
+        self.assertEqual(len(B.comments), 1)
+
+        # Update A to add A->B (a cycle).
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.url)
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+
+        # Dependency cycle injected so zuul should not have reported again on A
+        self.assertEqual(A.reported, 1)
+
+        # Now if we update B to remove the depends-on, everything
+        # should be okay.  B; A->B
+
+        B.addCommit()
+        B.editBody('')
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+
+        # Cycle was removed so now zuul should have reported again on A
+        self.assertEqual(A.reported, 2)
+
+        self.fake_github.emitEvent(B.getPullRequestEditedEvent())
+        self.waitUntilSettled()
+        self.assertEqual(len(B.comments), 2)
diff --git a/zuul/driver/gerrit/gerritsource.py b/zuul/driver/gerrit/gerritsource.py
index 9a75b3e..9e327b9 100644
--- a/zuul/driver/gerrit/gerritsource.py
+++ b/zuul/driver/gerrit/gerritsource.py
@@ -70,13 +70,15 @@
         return change
 
     def getChangesDependingOn(self, change, projects):
+        changes = []
+        if not change.uris:
+            return changes
         queries = set()
         for uri in change.uris:
             queries.add('message:%s' % uri)
         query = '(' + ' OR '.join(queries) + ')'
         results = self.connection.simpleQuery(query)
         seen = set()
-        changes = []
         for result in results:
             for match in find_dependency_headers(result['commitMessage']):
                 found = False
diff --git a/zuul/driver/github/githubconnection.py b/zuul/driver/github/githubconnection.py
index 1957cc2..a7aefe0 100644
--- a/zuul/driver/github/githubconnection.py
+++ b/zuul/driver/github/githubconnection.py
@@ -646,9 +646,12 @@
         return self._github
 
     def maintainCache(self, relevant):
+        remove = set()
         for key, change in self._change_cache.items():
             if change not in relevant:
-                del self._change_cache[key]
+                remove.add(key)
+        for key in remove:
+            del self._change_cache[key]
 
     def getChange(self, event, refresh=False):
         """Get the change representing an event."""
@@ -661,7 +664,6 @@
             change.uris = [
                 '%s/%s/pull/%s' % (self.server, project, change.number),
             ]
-            change.updated_at = self._ghTimestampToDate(event.updated_at)
             change.source_event = event
             change.is_current_patchset = (change.pr.get('head').get('sha') ==
                                           event.patch_number)
@@ -789,6 +791,8 @@
         change.labels = change.pr.get('labels')
         # ensure message is at least an empty string
         change.message = change.pr.get('body') or ''
+        change.updated_at = self._ghTimestampToDate(
+            change.pr.get('updated_at'))
 
         if history is None:
             history = []
diff --git a/zuul/driver/github/githubsource.py b/zuul/driver/github/githubsource.py
index 9834727..33f8f7c 100644
--- a/zuul/driver/github/githubsource.py
+++ b/zuul/driver/github/githubsource.py
@@ -46,6 +46,8 @@
         if not change.number:
             # Not a pull request, considering merged.
             return True
+        # We don't need to perform another query because the API call
+        # to perform the merge will ensure this is updated.
         return change.is_merged
 
     def canMerge(self, change, allow_needs):
diff --git a/zuul/manager/dependent.py b/zuul/manager/dependent.py
index 23c2cdb..20b376d 100644
--- a/zuul/manager/dependent.py
+++ b/zuul/manager/dependent.py
@@ -166,7 +166,6 @@
         # Return true if okay to proceed enqueing this change,
         # false if the change should not be enqueued.
         self.log.debug("Checking for changes needed by %s:" % change)
-        source = change.project.source
         if (hasattr(change, 'commit_needs_changes') and
             (change.refresh_deps or change.commit_needs_changes is None)):
             self.updateCommitDependencies(change, change_queue)
@@ -201,7 +200,8 @@
                     self.log.debug("  Needed change is already ahead "
                                    "in the queue")
                     continue
-                if source.canMerge(needed_change, self.getSubmitAllowNeeds()):
+                if needed_change.project.source.canMerge(
+                        needed_change, self.getSubmitAllowNeeds()):
                     self.log.debug("  Change %s is needed" % needed_change)
                     if needed_change not in changes_needed:
                         changes_needed.append(needed_change)