diff --git a/rest_framework/viewsets.py b/rest_framework/viewsets.py
index d94c81df4..244c14d39 100644
--- a/rest_framework/viewsets.py
+++ b/rest_framework/viewsets.py
@@ -25,11 +25,12 @@ from django.utils.decorators import classonlymethod
 from django.views.decorators.csrf import csrf_exempt
 
 from rest_framework import generics, mixins, views
+from rest_framework.decorators import MethodMapper
 from rest_framework.reverse import reverse
 
 
 def _is_extra_action(attr):
-    return hasattr(attr, 'mapping')
+    return hasattr(attr, 'mapping') and isinstance(attr.mapping, MethodMapper)
 
 
 class ViewSetMixin:
diff --git a/tests/test_viewsets.py b/tests/test_viewsets.py
index fc62cc981..921daf186 100644
--- a/tests/test_viewsets.py
+++ b/tests/test_viewsets.py
@@ -90,7 +90,6 @@ class ActionViewSetWithMapping(ActionViewSet):
     mapper = ThingWithMapping()
 
 
-
 router = SimpleRouter()
 router.register(r'actions', ActionViewSet)
 router.register(r'actions-alt', ActionViewSet, basename='actions-alt')
@@ -156,6 +155,7 @@ class InitializeViewSetsTestCase(TestCase):
             self.assertNotIn(attribute, dir(bare_view))
             self.assertIn(attribute, dir(view))
 
+
 class GetExtraActionsTests(TestCase):
 
     def test_extra_actions(self):