diff --git a/djangorestframework/mixins.py b/djangorestframework/mixins.py
index 7f0870f85..2ea5e8404 100644
--- a/djangorestframework/mixins.py
+++ b/djangorestframework/mixins.py
@@ -507,11 +507,6 @@ class ModelMixin(object):
         if BaseRenderer._FORMAT_QUERY_PARAM in tmp:
             del tmp[BaseRenderer._FORMAT_QUERY_PARAM]
 
-        if args:
-            # If we have any no kwargs then assume the last arg represents the
-            # primrary key. Otherwise assume the kwargs uniquely identify the
-            # model.
-            tmp.update({'pk': args[-1]})
         return Q(**tmp)
 
     def get_instance_data(self, model, content, **kwargs):