diff --git a/django_pdb/middleware.py b/django_pdb/middleware.py
index 58f0554..0f38a54 100644
--- a/django_pdb/middleware.py
+++ b/django_pdb/middleware.py
@@ -38,7 +38,10 @@ def __init__(self, get_response=None, debug_only=True):
         unless settings.DEBUG is also True. Otherwise, this middleware
         is always active.
         """
-        self.get_response = get_response
+        if parent is object:  # compatibility
+            self.get_response = get_response
+        else:
+            super().__init__(get_response)
         if debug_only and not settings.DEBUG:
             raise MiddlewareNotUsed()