diff --git a/py-polars/tests/unit/operations/map/test_map_groups.py b/py-polars/tests/unit/operations/map/test_map_groups.py
index 5432f001a238..717b35303842 100644
--- a/py-polars/tests/unit/operations/map/test_map_groups.py
+++ b/py-polars/tests/unit/operations/map/test_map_groups.py
@@ -162,6 +162,6 @@ def foo(x: pl.Series) -> pl.Series:
         pl.DataFrame({"key": [0, 0, 1], "a": [None, None, None]})
         .group_by("key")
         .agg(pl.map_groups(exprs=["a"], function=foo))  # type: ignore[arg-type]
-        .sort("a"),
+        .sort("key"),
         pl.DataFrame({"key": [0, 1], "a": [None, None]}),
     )