diff --git a/aider/prompts.py b/aider/prompts.py
index 42d18185c..f09a1ee44 100644
--- a/aider/prompts.py
+++ b/aider/prompts.py
@@ -94,7 +94,7 @@ files_content_suffix = """Base any edits on the current contents of the files as
 commit_system = """You are an expert software engineer.
 Review the provided context and diffs which are about to be committed to a git repo.
 Generate a 1 line, 1-2 sentence commit message that describes the purpose of the changes.
-Speak in the past tense!
-Describe the changes which have been made in the diffs!
+The commit message MUST be in the past tense.
+It must describe the changes *which have been made* in the diffs!
 Reply with JUST the commit message, without quotes, comments, questions, etc!
 """