diff --git a/lib/couchrest/more/casted_model.rb b/lib/couchrest/more/casted_model.rb
index ab0bbf7..8ab794e 100644
--- a/lib/couchrest/more/casted_model.rb
+++ b/lib/couchrest/more/casted_model.rb
@@ -9,7 +9,8 @@ module CouchRest
     end
     
     def initialize(keys={})
-      super
+      raise StandardError unless self.is_a? Hash
+      super()
       keys.each do |k,v|
         self[k.to_s] = v
       end if keys
diff --git a/spec/couchrest/more/casted_model_spec.rb b/spec/couchrest/more/casted_model_spec.rb
index a2b9216..82558c1 100644
--- a/spec/couchrest/more/casted_model_spec.rb
+++ b/spec/couchrest/more/casted_model_spec.rb
@@ -4,6 +4,7 @@ require File.join(FIXTURE_PATH, 'more', 'card')
 class WithCastedModelMixin < Hash
   include CouchRest::CastedModel
   property :name
+  property :no_value
 end
 
 class DummyModel < CouchRest::ExtendedDocument
@@ -54,6 +55,14 @@ describe CouchRest::CastedModel do
     it "should know who casted it" do
       @casted_obj.casted_by.should == @obj
     end
+
+    it "should return nil for the 'no_value' attribute" do
+      @casted_obj.no_value.should be_nil
+    end
+
+    it "should return nil for the unknown attribute" do
+      @casted_obj["unknown"].should be_nil
+    end
   end
   
   describe "casted as an array of a different type" do