1 files changed, 16 insertions, 4 deletions
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 5bec68ce4f6..9a7e66a9cbb 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -375,15 +375,27 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def diff_start_sha
-    diff_start_commit.try(:sha)
+    if persisted?
+      merge_request_diff.start_commit_sha
+    else
+      target_branch_head.try(:sha)
+    end
   end
 
   def diff_base_sha
-    diff_base_commit.try(:sha)
+    if persisted?
+      merge_request_diff.base_commit_sha
+    else
+      branch_merge_base_commit.try(:sha)
+    end
   end
 
   def diff_head_sha
-    diff_head_commit.try(:sha)
+    if persisted?
+      merge_request_diff.head_commit_sha
+    else
+      source_branch_head.try(:sha)
+    end
   end
 
   # When importing a pull request from GitHub, the old and new branches may no
@@ -646,7 +658,7 @@ class MergeRequest < ActiveRecord::Base
     !ProtectedBranch.protected?(source_project, source_branch) &&
       !source_project.root_ref?(source_branch) &&
       Ability.allowed?(current_user, :push_code, source_project) &&
-      diff_head_commit == source_branch_head
+      diff_head_sha == source_branch_head.try(:sha)
   end
 
   def should_remove_source_branch?