diff --git a/opentech/apply/funds/models/submissions.py b/opentech/apply/funds/models/submissions.py
index 8543f23fe765ef6b826fd093ed5eb071013960f9..cd1c4152330e07aa3e251b2500d0a6639e1feaf2 100644
--- a/opentech/apply/funds/models/submissions.py
+++ b/opentech/apply/funds/models/submissions.py
@@ -631,7 +631,7 @@ class ApplicationSubmission(
         reviewers_submitted = self.assigned.reviewed().values('reviewer')
         reviewers = self.reviewers.exclude(id__in=reviewers_submitted)
         partners = self.partners.exclude(id__in=reviewers_submitted)
-        return reviewers | partners
+        return reviewers.union(partners)
 
     @property
     def staff_not_reviewed(self):