diff --git a/tests/test_black.py b/tests/test_black.py
index 899cbeb111d..23815da9042 100644
--- a/tests/test_black.py
+++ b/tests/test_black.py
@@ -317,7 +317,7 @@ def test_expression_diff(self) -> None:
             msg = (
                 "Expected diff isn't equal to the actual. If you made changes to"
                 " expression.py and this is an anticipated difference, overwrite"
-                f" tests/data/expression.diff with {dump}"
+                f" tests/data/cases/expression.diff with {dump}"
             )
             self.assertEqual(expected, actual, msg)