fix 64-bit

Manual casting is necessary for 64-bit to work correctly.

see: http://stackoverflow.com/questions/19507456/sudzc-arc-version-objc-msgsend-call-causes-exc-bad-access-using-64-bit-archite

and: https://developer.apple.com/library/ios/documentation/General/Conceptual/CocoaTouch64BitGuide/ConvertingYourAppto64-Bit/ConvertingYourAppto64-Bit.html