diff --git a/lib/ap/mixin/mongo_mapper.rb b/lib/ap/mixin/mongo_mapper.rb
index 9b105ee..cb856a7 100644
--- a/lib/ap/mixin/mongo_mapper.rb
+++ b/lib/ap/mixin/mongo_mapper.rb
@@ -44,7 +44,7 @@ module AwesomePrintMongoMapper
     return object.inspect if !defined?(ActiveSupport::OrderedHash) || !object.respond_to?(:keys)
 
     data = object.keys.inject(ActiveSupport::OrderedHash.new) do |hash, c|
-      hash[c.first] = c.last.type.to_s.underscore.intern
+      hash[c.first] = (c.last.type || "undefined").to_s.underscore.intern
       hash
     end
     "class #{object} < #{object.superclass} " << awesome_hash(data)
diff --git a/spec/mongo_mapper_spec.rb b/spec/mongo_mapper_spec.rb
index 7d429f7..ae2499b 100644
--- a/spec/mongo_mapper_spec.rb
+++ b/spec/mongo_mapper_spec.rb
@@ -38,6 +38,20 @@ class User < Object {
      "last_name" => :string,
     "first_name" => :string
 }
+EOS
+    end
+
+    it "should print for a class when type is undefined" do
+      class Chamelion
+        include MongoMapper::Document
+        key :last_attribute
+      end
+
+      @ap.send(:awesome, Chamelion).should == <<-EOS.strip
+class Chamelion < Object {
+               "_id" => :object_id,
+    "last_attribute" => :undefined
+}
 EOS
     end
   end