diff --git a/lib/json-schema/attributes/type.rb b/lib/json-schema/attributes/type.rb
index e8ad4637..fd60a440 100644
--- a/lib/json-schema/attributes/type.rb
+++ b/lib/json-schema/attributes/type.rb
@@ -57,13 +57,13 @@ def self.validate(current_schema, data, fragments, processor, validator, options
           end
         elsif !valid
           if union
-            message = "The property '#{build_fragment(fragments)}' of type #{data.class} did not match one or more of the following types:"
+            message = "The property '#{build_fragment(fragments)}' of type #{type_of_data(data)} did not match one or more of the following types:"
             types.each {|type| message += type.is_a?(String) ? " #{type}," : " (schema)," }
             message.chop!
             validation_error(processor, message, fragments, current_schema, self, options[:record_errors])
             validation_errors(processor).last.sub_errors = union_errors
           else
-            message = "The property '#{build_fragment(fragments)}' of type #{data.class} did not match the following type:"
+            message = "The property '#{build_fragment(fragments)}' of type #{type_of_data(data)} did not match the following type:"
             types.each {|type| message += type.is_a?(String) ? " #{type}," : " (schema)," }
             message.chop!
             validation_error(processor, message, fragments, current_schema, self, options[:record_errors])            
@@ -86,6 +86,18 @@ def self.data_valid_for_type?(data, type)
         valid_classes = TYPE_CLASS_MAPPINGS.fetch(type) { return true }
         Array(valid_classes).any? { |c| data.is_a?(c) }
       end
+
+      # Lookup Schema type of given class instance
+      def self.type_of_data(data)
+        type, klass = TYPE_CLASS_MAPPINGS.map { |k,v| [k,v] }.sort_by { |i|
+          k,v = i
+          -Array(v).map { |klass| klass.ancestors.size }.max
+        }.find { |i|
+          k,v = i
+          Array(v).any? { |klass| data.kind_of?(klass) }
+        }
+        type
+      end
     end
   end
-end
\ No newline at end of file
+end
diff --git a/lib/json-schema/schema.rb b/lib/json-schema/schema.rb
index 51f4593e..29c6f003 100644
--- a/lib/json-schema/schema.rb
+++ b/lib/json-schema/schema.rb
@@ -10,7 +10,7 @@ def initialize(schema,uri,parent_validator=nil)
       @uri = uri
       
       # If there is an ID on this schema, use it to generate the URI
-      if @schema['id']
+      if @schema['id'] && @schema['id'].kind_of?(String)
         temp_uri = URI.parse(@schema['id'])
         if temp_uri.relative?
           uri = uri.merge(@schema['id'])
diff --git a/test/test_schema_type_attribute.rb b/test/test_schema_type_attribute.rb
new file mode 100644
index 00000000..0f612c9b
--- /dev/null
+++ b/test/test_schema_type_attribute.rb
@@ -0,0 +1,21 @@
+require 'test/unit'
+require File.dirname(__FILE__) + '/../lib/json-schema'
+
+class TestSchemaTypeAttribute < Test::Unit::TestCase
+  def test_type_of_data
+    assert_equal(type_of_data(String.new), 'string')
+    assert_equal(type_of_data(Numeric.new), 'number')
+    assert_equal(type_of_data(1), 'integer')
+    assert_equal(type_of_data(true), 'boolean')
+    assert_equal(type_of_data(false), 'boolean')
+    assert_equal(type_of_data(Hash.new), 'object')
+    assert_equal(type_of_data(nil), 'null')
+    assert_equal(type_of_data(Object.new), 'any')
+  end
+
+  private
+
+  def type_of_data(data)
+    JSON::Schema::TypeAttribute.type_of_data(data)
+  end
+end