diff --git a/aider/commands.py b/aider/commands.py
index d429bf5cd..f6e84a3c4 100644
--- a/aider/commands.py
+++ b/aider/commands.py
@@ -188,7 +188,7 @@ class Commands:
 
         last_commit = self.coder.repo.repo.head.commit
         dump(last_commit)
-        changed_files_last_commit = {item.a_path for item in last_commit.diff(None)}
+        changed_files_last_commit = {item.a_path for item in last_commit.diff(last_commit.parents[0])}
         dirty_files = [item.a_path for item in self.coder.repo.repo.index.diff(None)]
         dirty_files_in_last_commit = changed_files_last_commit.intersection(dirty_files)
         dump(changed_files_last_commit)