diff --git a/src/pytest_cases/fixture_parametrize_plus.py b/src/pytest_cases/fixture_parametrize_plus.py
index 6234d153..13597d09 100644
--- a/src/pytest_cases/fixture_parametrize_plus.py
+++ b/src/pytest_cases/fixture_parametrize_plus.py
@@ -613,7 +613,7 @@ def nostyle(cls,
 _IDGEN = object()
 
 
-def parametrize(argnames=None,   # type: str
+def parametrize(argnames=None,   # type: Union[str, List[str]]
                 argvalues=None,  # type: Iterable[Any]
                 indirect=False,  # type: bool
                 ids=None,        # type: Union[Callable, Iterable[str]]