diff --git a/aider/commands.py b/aider/commands.py
index 5c016381a..1dd429eb0 100644
--- a/aider/commands.py
+++ b/aider/commands.py
@@ -306,6 +306,10 @@ class Commands:
             return
 
         last_commit = self.coder.repo.repo.head.commit
+        if not last_commit.parents:
+            self.io.tool_error("This is the first commit in the repository. Cannot undo.")
+            return
+
         prev_commit = last_commit.parents[0]
         changed_files_last_commit = [item.a_path for item in last_commit.diff(prev_commit)]
 
diff --git a/tests/basic/test_commands.py b/tests/basic/test_commands.py
index f0be96232..abbcfecfc 100644
--- a/tests/basic/test_commands.py
+++ b/tests/basic/test_commands.py
@@ -617,6 +617,13 @@ class TestCommands(TestCase):
             # Attempt to undo the last commit
             commands.cmd_undo("")
 
+            # Check that the commit is still present
+            self.assertEqual(last_commit_hash, repo.head.commit.hexsha[:7])
+            self.assertTrue(file_path.exists())
+
+            # Check that an error message was displayed
+            self.assertIn("This is the first commit in the repository. Cannot undo.", io.get_last_error())
+
             # Check that the last commit is still present
             self.assertEqual(last_commit_hash, repo.head.commit.hexsha[:7])
             self.assertTrue(file_path.exists())