diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 926944bc3b3ea44626653b05b3f4beefeff08b0f..70005a87f4bfb23c43e71d06879bd0e0b06a98b0 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -221,7 +221,7 @@ class MergeRequest < ActiveRecord::Base
   # true base commit, so we can't simply have `#diff_base_commit` fall back on
   # this method.
   def likely_diff_base_commit
-    first_commit.parent || first_commit
+    first_commit.try(:parent) || first_commit
   end
 
   def diff_start_commit