diff --git a/treeherder/model/derived/jobs.py b/treeherder/model/derived/jobs.py
index <HASH>..<HASH> 100644
--- a/treeherder/model/derived/jobs.py
+++ b/treeherder/model/derived/jobs.py
@@ -195,7 +195,7 @@ class JobsModel(TreeherderModelBase):
         if not project:
             project = self.project
         build_systems = cache.get("build_system_by_repo", None)
-        if not build_systems:
+        if not build_systems or project not in build_systems:
             build_systems = dict((repo, build_system_type) for repo, build_system_type in
                 ReferenceDataSignatures.objects.order_by("repository"
                 ).values_list("repository", "build_system_type").distinct()
Bug <I> - Delete build system cached list when project is not found