Index: src/main/org/codehaus/groovy/runtime/metaclass/MixinInstanceMetaMethod.java
===================================================================
--- src/main/org/codehaus/groovy/runtime/metaclass/MixinInstanceMetaMethod.java	(revision 18239)
+++ src/main/org/codehaus/groovy/runtime/metaclass/MixinInstanceMetaMethod.java	(working copy)
@@ -33,6 +33,7 @@
     }
 
     public Object invoke(Object object, Object[] arguments) {
+        arguments = method.correctArguments(arguments);
         final Object result = method.invoke(mixinInMetaClass.getMixinInstance(object), arguments);
         return result;
     }