diff --git a/lib/mongo/util/core_ext.rb b/lib/mongo/util/core_ext.rb
index ff357fc..5e8f829 100644
--- a/lib/mongo/util/core_ext.rb
+++ b/lib/mongo/util/core_ext.rb
@@ -31,7 +31,7 @@ class Hash
   #:nodoc:
   def assert_valid_keys(*valid_keys)
     unknown_keys = keys - [valid_keys].flatten
-    raise(Mongo::MongoArgumentError, "Unknown key(s): #{unknown_keys.join(", ")}") unless unknown_keys.empty?
+    raise(ArgumentError, "Unknown key(s): #{unknown_keys.join(", ")}") unless unknown_keys.empty?
   end
 
 end