diff --git a/rest_framework/utils/timezone.py b/rest_framework/utils/timezone.py
index 3fb34c8fa..e4cf5b022 100644
--- a/rest_framework/utils/timezone.py
+++ b/rest_framework/utils/timezone.py
@@ -18,6 +18,6 @@ def datetime_ambiguous(dt):
     )
 
 
-def valid_datetime(dt) -> bool:
+def valid_datetime(dt):
     """Returns True if the datetime is not ambiguous or imaginary, False otherwise."""
     return isinstance(dt.tzinfo, tzinfo) and not datetime_ambiguous(dt)