diff --git a/tests/fixtures/layout-live-reconfiguration-del-project.yaml b/tests/fixtures/layout-live-reconfiguration-del-project.yaml
new file mode 100644
index 0000000..07ffb2e
--- /dev/null
+++ b/tests/fixtures/layout-live-reconfiguration-del-project.yaml
@@ -0,0 +1,21 @@
+pipelines:
+  - name: check
+    manager: IndependentPipelineManager
+    trigger:
+      gerrit:
+        - event: patchset-created
+    success:
+      gerrit:
+        verified: 1
+    failure:
+      gerrit:
+        verified: -1
+
+projects:
+  - name: org/project
+    merge-mode: cherry-pick
+    check:
+      - project-merge:
+        - project-test1
+        - project-test2
+        - project-testfile
diff --git a/tests/test_scheduler.py b/tests/test_scheduler.py
index 61a2d09..7ed7efb 100755
--- a/tests/test_scheduler.py
+++ b/tests/test_scheduler.py
@@ -2494,6 +2494,57 @@
         # Ensure the removed job was not included in the report.
         self.assertNotIn('project1-project2-integration', A.messages[0])
 
+    def test_live_reconfiguration_del_project(self):
+        # Test project deletion from layout
+        # while changes are enqueued
+
+        self.worker.hold_jobs_in_build = True
+        A = self.fake_gerrit.addFakeChange('org/project', 'master', 'A')
+        B = self.fake_gerrit.addFakeChange('org/project1', 'master', 'B')
+        C = self.fake_gerrit.addFakeChange('org/project1', 'master', 'C')
+
+        # A Depends-On: B
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.data['id'])
+        self.fake_gerrit.addEvent(B.addApproval('APRV', 1))
+
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.fake_gerrit.addEvent(C.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.worker.release('.*-merge')
+        self.waitUntilSettled()
+        self.assertEqual(len(self.builds), 5)
+
+        # This layout defines only org/project, not org/project1
+        self.config.set('zuul', 'layout_config',
+                        'tests/fixtures/layout-live-'
+                        'reconfiguration-del-project.yaml')
+        self.sched.reconfigure(self.config)
+        self.waitUntilSettled()
+
+        # Builds for C aborted, builds for A succeed,
+        # and have change B applied ahead
+        job_c = self.getJobFromHistory('project1-test1')
+        self.assertEqual(job_c.changes, '3,1')
+        self.assertEqual(job_c.result, 'ABORTED')
+
+        self.worker.hold_jobs_in_build = False
+        self.worker.release()
+        self.waitUntilSettled()
+
+        self.assertEqual(self.getJobFromHistory('project-test1').changes,
+                         '2,1 1,1')
+
+        self.assertEqual(A.data['status'], 'NEW')
+        self.assertEqual(B.data['status'], 'NEW')
+        self.assertEqual(C.data['status'], 'NEW')
+        self.assertEqual(A.reported, 1)
+        self.assertEqual(B.reported, 0)
+        self.assertEqual(C.reported, 0)
+
+        self.assertEqual(len(self.sched.layout.pipelines['check'].queues), 0)
+        self.assertIn('Build succeeded', A.messages[0])
+
     def test_live_reconfiguration_functions(self):
         "Test live reconfiguration with a custom function"
         self.worker.registerFunction('build:node-project-test1:debian')
@@ -3668,6 +3719,48 @@
         self.assertEqual(A.data['status'], 'NEW')
         self.assertEqual(B.data['status'], 'NEW')
 
+    def test_crd_gate_unknown(self):
+        "Test unknown projects in dependent pipeline"
+        self.init_repo("org/unknown")
+        A = self.fake_gerrit.addFakeChange('org/project', 'master', 'A')
+        B = self.fake_gerrit.addFakeChange('org/unknown', 'master', 'B')
+        A.addApproval('CRVW', 2)
+        B.addApproval('CRVW', 2)
+
+        # A Depends-On: B
+        A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
+            A.subject, B.data['id'])
+
+        B.addApproval('APRV', 1)
+        self.fake_gerrit.addEvent(A.addApproval('APRV', 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.assertEqual(B.data['status'], 'NEW')
+        self.assertEqual(A.reported, 0)
+        self.assertEqual(B.reported, 0)
+        self.assertEqual(len(self.history), 0)
+
+        # Simulate change B being gated outside this layout
+        self.fake_gerrit.addEvent(B.addApproval('APRV', 1))
+        B.setMerged()
+        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('APRV', 1))
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'MERGED')
+        self.assertEqual(A.reported, 2)
+        self.assertEqual(B.data['status'], 'MERGED')
+        self.assertEqual(B.reported, 0)
+
     def test_crd_check(self):
         "Test cross-repo dependencies in independent pipelines"
 
@@ -3782,12 +3875,12 @@
         self.assertIn('Build succeeded', A.messages[0])
         self.assertIn('Build succeeded', B.messages[0])
 
-    def test_crd_check_reconfiguration(self):
+    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('org/project1', 'master', 'A')
-        B = self.fake_gerrit.addFakeChange('org/project2', 'master', 'B')
+        A = self.fake_gerrit.addFakeChange(project1, 'master', 'A')
+        B = self.fake_gerrit.addFakeChange(project2, 'master', 'B')
 
         # A Depends-On: B
         A.data['commitMessage'] = '%s\n\nDepends-On: %s\n' % (
@@ -3820,6 +3913,17 @@
         self.assertEqual(self.history[0].changes, '2,1 1,1')
         self.assertEqual(len(self.sched.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("org/unknown")
+        self._test_crd_check_reconfiguration('org/project1', 'org/unknown')
+
     def test_crd_check_ignore_dependencies(self):
         "Test cross-repo dependencies can be ignored"
         self.config.set('zuul', 'layout_config',
diff --git a/zuul/model.py b/zuul/model.py
index f8e0d25..3a228f5 100644
--- a/zuul/model.py
+++ b/zuul/model.py
@@ -431,9 +431,13 @@
 
 
 class Project(object):
-    def __init__(self, name):
+    def __init__(self, name, foreign=False):
         self.name = name
         self.merge_mode = MERGER_MERGE_RESOLVE
+        # foreign projects are those referenced in dependencies
+        # of layout projects, this should matter
+        # when deciding whether to enqueue their changes
+        self.foreign = foreign
 
     def __str__(self):
         return self.name
diff --git a/zuul/scheduler.py b/zuul/scheduler.py
index a9bd6b2..4375f98 100644
--- a/zuul/scheduler.py
+++ b/zuul/scheduler.py
@@ -507,11 +507,15 @@
             name = reporter.name
         self.reporters[name] = reporter
 
-    def getProject(self, name):
+    def getProject(self, name, create_foreign=False):
         self.layout_lock.acquire()
         p = None
         try:
             p = self.layout.projects.get(name)
+            if p is None and create_foreign:
+                self.log.info("Registering foreign project: %s" % name)
+                p = Project(name, foreign=True)
+                self.layout.projects[name] = p
         finally:
             self.layout_lock.release()
         return p
@@ -685,15 +689,15 @@
                         item.items_behind = []
                         item.pipeline = None
                         item.queue = None
-                        project = layout.projects.get(item.change.project.name)
-                        if not project:
-                            self.log.warning("Unable to find project for "
-                                             "change %s while reenqueueing" %
-                                             item.change)
-                            item.change.project = None
-                            items_to_remove.append(item)
-                            continue
-                        item.change.project = project
+                        project_name = item.change.project.name
+                        item.change.project = layout.projects.get(project_name)
+                        if not item.change.project:
+                            self.log.debug("Project %s not defined, "
+                                           "re-instantiating as foreign" %
+                                           project_name)
+                            project = Project(project_name, foreign=True)
+                            layout.projects[project_name] = project
+                            item.change.project = project
                         item_jobs = new_pipeline.getJobs(item)
                         for build in item.current_build_set.getBuilds():
                             job = layout.jobs.get(build.job.name)
@@ -861,7 +865,7 @@
         self.log.debug("Processing trigger event %s" % event)
         try:
             project = self.layout.projects.get(event.project_name)
-            if not project:
+            if not project or project.foreign:
                 self.log.debug("Project %s not found" % event.project_name)
                 return
 
@@ -1797,10 +1801,11 @@
         if existing:
             return DynamicChangeQueueContextManager(existing)
         if change.project not in self.pipeline.getProjects():
-            return DynamicChangeQueueContextManager(None)
+            self.pipeline.addProject(change.project)
         change_queue = ChangeQueue(self.pipeline)
         change_queue.addProject(change.project)
         self.pipeline.addQueue(change_queue)
+        self.log.debug("Dynamically created queue %s", change_queue)
         return DynamicChangeQueueContextManager(change_queue)
 
     def enqueueChangesAhead(self, change, quiet, ignore_requirements,
diff --git a/zuul/trigger/gerrit.py b/zuul/trigger/gerrit.py
index 175e3f8..05d7581 100644
--- a/zuul/trigger/gerrit.py
+++ b/zuul/trigger/gerrit.py
@@ -94,7 +94,7 @@
                     Can not get account information." % event.type)
             event.account = None
 
-        if event.change_number:
+        if event.change_number and self.sched.getProject(event.project_name):
             # Call _getChange for the side effect of updating the
             # cache.  Note that this modifies Change objects outside
             # the main thread.
@@ -404,7 +404,11 @@
         if 'project' not in data:
             raise Exception("Change %s,%s not found" % (change.number,
                                                         change.patchset))
-        change.project = self.sched.getProject(data['project'])
+        # If updated changed came as a dependent on
+        # and its project is not defined,
+        # then create a 'foreign' project for it in layout
+        change.project = self.sched.getProject(data['project'],
+                                               create_foreign=bool(history))
         change.branch = data['branch']
         change.url = data['url']
         max_ps = 0