diff --git a/pagure/lib/git.py b/pagure/lib/git.py
index 81ece74..8a47677 100644
--- a/pagure/lib/git.py
+++ b/pagure/lib/git.py
@@ -1282,6 +1282,11 @@ def diff_pull_request(
     if branch:
         commitid = branch.get_object().hex
 
+    if request.branch not in orig_repo.listall_branches():
+        raise pagure.exceptions.PagureException(
+            'The branch into which this pull-request was to be merged : %s '
+            'seems to no longer present in this repo' % request.branch)
+
     if not repo_obj.is_empty and not orig_repo.is_empty:
         # Pull-request open
         master_commits = [