diff --git a/aider/coders/base_coder.py b/aider/coders/base_coder.py
index 28ac3360b..73f87b49f 100755
--- a/aider/coders/base_coder.py
+++ b/aider/coders/base_coder.py
@@ -1327,7 +1327,7 @@ class Coder:
 
         added_fnames = []
         group = ConfirmGroup(new_mentions)
-        for rel_fname in new_mentions:
+        for rel_fname in sorted(new_mentions):
             if self.io.confirm_ask(f"Add {rel_fname} to the chat?", group=group):
                 self.add_rel_fname(rel_fname)
                 added_fnames.append(rel_fname)
diff --git a/tests/basic/test_coder.py b/tests/basic/test_coder.py
index 2a4aa8ae4..e72baf1ab 100644
--- a/tests/basic/test_coder.py
+++ b/tests/basic/test_coder.py
@@ -199,13 +199,13 @@ class TestCoder(unittest.TestCase):
             coder = Coder.create(self.GPT35, None, io)
 
             # Mock get_file_mentions to return two file names
-            coder.get_file_mentions = MagicMock(return_value=["file1.txt", "file2.txt"])
+            coder.get_file_mentions = MagicMock(return_value=set(["file1.txt", "file2.txt"]))
 
             # Mock confirm_ask to return False for the first call and True for the second
-            io.confirm_ask = MagicMock(side_effect=[False, True])
+            io.confirm_ask = MagicMock(side_effect=[False, True, True])
 
             # First call to check_for_file_mentions
-            coder.check_for_file_mentions("Please check file1.txt and file2.txt")
+            coder.check_for_file_mentions("Please check file1.txt for the info")
 
             # Assert that confirm_ask was called twice
             self.assertEqual(io.confirm_ask.call_count, 2)