diff --git a/zuul/configloader.py b/zuul/configloader.py
index d3f3236..7a0b12e 100644
--- a/zuul/configloader.py
+++ b/zuul/configloader.py
@@ -1300,7 +1300,10 @@
     def _resolveShadowProjects(self, tenant, tpc):
         shadow_projects = []
         for sp in tpc.shadow_projects:
-            shadow_projects.append(tenant.getProject(sp)[1])
+            _, project = tenant.getProject(sp)
+            if project is None:
+                raise ProjectNotFoundError(sp)
+            shadow_projects.append(project)
         tpc.shadow_projects = frozenset(shadow_projects)
 
     def _getProjectBranches(self, tenant, tpc, old_tenant):