diff --git a/lib/shoulda/matchers/active_model/allow_mass_assignment_of_matcher.rb b/lib/shoulda/matchers/active_model/allow_mass_assignment_of_matcher.rb
index 84fa1f44..cdac0677 100644
--- a/lib/shoulda/matchers/active_model/allow_mass_assignment_of_matcher.rb
+++ b/lib/shoulda/matchers/active_model/allow_mass_assignment_of_matcher.rb
@@ -61,23 +61,21 @@ module Shoulda # :nodoc:
         end
 
         def whitelisting?
-          !accessible_attributes.empty?
+          authorizer.kind_of?(::ActiveModel::MassAssignmentSecurity::WhiteList)
         end
 
         def attr_mass_assignable?
-          if whitelisting?
-            accessible_attributes.include?(@attribute)
-          else
-            !protected_attributes.include?(@attribute)
-          end
+          !authorizer.deny?(@attribute)
+        end
+
+        def authorizer
+          @subject.class.active_authorizer
         end
 
         def class_name
           @subject.class.name
         end
-
       end
-
     end
   end
 end
diff --git a/spec/shoulda/active_model/allow_mass_assignment_of_matcher_spec.rb b/spec/shoulda/active_model/allow_mass_assignment_of_matcher_spec.rb
index b5774518..60f029c2 100644
--- a/spec/shoulda/active_model/allow_mass_assignment_of_matcher_spec.rb
+++ b/spec/shoulda/active_model/allow_mass_assignment_of_matcher_spec.rb
@@ -71,4 +71,16 @@ describe Shoulda::Matchers::ActiveModel::AllowMassAssignmentOfMatcher do
     end
   end
 
+  context "an attribute on a class with all protected attributes" do
+    before do
+      define_model :example, :attr => :string do
+        attr_accessible
+      end
+      @model = Example.new
+    end
+
+    it "should reject being mass-assignable" do
+      @model.should_not allow_mass_assignment_of(:attr)
+    end
+  end
 end