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'])