diff --git a/app/models/merge_request_diff.rb b/app/models/merge_request_diff.rb
index 69a846da9bef7857b75bfdb88915772e331e8a7a..c1c27ccf3e58685824f08279c993238da26856bc 100644
--- a/app/models/merge_request_diff.rb
+++ b/app/models/merge_request_diff.rb
@@ -290,7 +290,7 @@ class MergeRequestDiff < ActiveRecord::Base
   end
 
   def keep_around_commits
-    [repository, merge_request.source_project.repository].each do |repo|
+    [repository, merge_request.source_project.repository].uniq.each do |repo|
       repo.keep_around(start_commit_sha)
       repo.keep_around(head_commit_sha)
       repo.keep_around(base_commit_sha)