diff --git a/pr_agent/git_providers/azuredevops_provider.py b/pr_agent/git_providers/azuredevops_provider.py
index b9d2f3990c..c73a83540a 100644
--- a/pr_agent/git_providers/azuredevops_provider.py
+++ b/pr_agent/git_providers/azuredevops_provider.py
@@ -198,7 +198,7 @@ def get_diff_files(self) -> list[FilePatchInfo]:
                 return self.diff_files
 
             base_sha = self.pr.last_merge_target_commit
-            head_sha = self.pr.last_merge_commit
+            head_sha = getattr(self.pr, 'last_merge_source_commit', None) or self.pr.last_merge_commit
 
             # Get PR iterations
             iterations = self.azure_devops_client.get_pull_request_iterations(