diff --git a/AUTHORS b/AUTHORS
index 2b8af2b97..22b12ba9a 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -17,6 +17,7 @@ Garcia Solero <garciasolero>
 Tom Drummond <devioustree>
 Danilo Bargen <gwrtheyrn>
 Andrew McCloud <amccloud>
+Thomas Steinacher <thomasst>
 
 THANKS TO:
 
diff --git a/djangorestframework/permissions.py b/djangorestframework/permissions.py
index 59c5f481f..0052a6094 100644
--- a/djangorestframework/permissions.py
+++ b/djangorestframework/permissions.py
@@ -73,7 +73,7 @@ class IsAdminUser(BasePermission):
     """
 
     def check_permission(self, user):
-        if not user.is_staff():
+        if not user.is_staff:
             raise _403_FORBIDDEN_RESPONSE
 
 
diff --git a/djangorestframework/serializer.py b/djangorestframework/serializer.py
index 6803cb74c..582de70a1 100644
--- a/djangorestframework/serializer.py
+++ b/djangorestframework/serializer.py
@@ -106,7 +106,8 @@ class Serializer(object):
 
 
     def __init__(self, depth=None, stack=[], **kwargs):
-        self.depth = depth or self.depth
+        if depth is not None:
+            self.depth = depth
         self.stack = stack