When assigned to a local variable or attribute, a closure with named parameters throws a verify error. However, if the closure is called directly upon creation (i.e. without intermediate assignment to a variable), then the call works without problems. The same holds true if in a script the Binding is used to store the closure reference instead of a variable. Here is a test case. The commented test methods throw the verify error. class ClosureNamedParameters extends GroovyTestCase { // void testClosureAsLocalVar() { // def local = { Map params -> // params.x * params.y // } // assert local(x : 2, y : 3) == 6 // } void testClosureDirectly() { assert { Map params -> params.x * params.y }(x : 2, y : 3) == 6 } // def attribute // void testClosureAsAttribute() { // attribute = { Map params ->// params.x * params.y// } } // assert attribute(x : 2, y : 3) == 6 // } }