diff --git a/src/drf_yasg/inspectors/field.py b/src/drf_yasg/inspectors/field.py
index 9f063b6..6527db4 100644
--- a/src/drf_yasg/inspectors/field.py
+++ b/src/drf_yasg/inspectors/field.py
@@ -610,7 +610,7 @@ class SerializerMethodFieldInspector(FieldInspector):
             # look for Python 3.5+ style type hinting of the return value
             hint_class = inspect_signature(method).return_annotation
 
-            if not issubclass(hint_class, inspect._empty):
+            if inspect.isclass(hint_class) and not issubclass(hint_class, inspect._empty):
                 type_info = get_basic_type_info_from_hint(hint_class)
 
                 if type_info is not None: