Is this a bug? I don't see anything quite like it in Trac. I have a binding to a button's state property. Here's the binding: @comboBox.bind 'enabled', toObject: @button, withKeyPath: 'state', options: { NSValueTransformerBindingOption => OffStateMeansTrueTransformer.alloc.init } At the point the binding is made, the state of the button is a fixnum 0. The value transformer is immediately called to set the starting value. Here's the transformedValue code: def transformedValue(state) puts "state -> bool transforming #{state.inspect}" # prints #<NSCFNumber:0x1022180> # state.intValue is 0 Because of this, I have to cast the state before making comparisons: case state.intValue when NSOffState then true when NSOnState then false else raise "The value to transform should be either NSOffState or NSOnState." end If this is a bug, I'll write a testcase. ----- Brian Marick, independent consultant Mostly on agile methods with a testing slant www.exampler.com, www.exampler.com/blog, www.twitter.com/marick