diff --git a/python/tests/test_fast.py b/python/tests/test_fast.py
index 518c26c70..5aabaf388 100644
--- a/python/tests/test_fast.py
+++ b/python/tests/test_fast.py
@@ -585,7 +585,7 @@ class TestFast(mlx_tests.MLXTestCase):
     def test_custom_kernel_basic(self):
         if mx.metal.is_available():
             source = """
-                uint elem thread_position_in_grid.x;
+                uint elem = thread_position_in_grid.x;
                 out1[elem] = a[elem];
             """
             custom_kernel = mx.fast.metal_kernel