object_getInstanceVariable works for float, int, bool, but not for double?

I've got object_getInstanceVariable to work as here however it seems to only work for floats, bools and ints not doubles. I do suspect I'm doing something wrong but I've been going in circles with this. float myFloatValue; float someFloat = 2.123f; object_getInstanceVariable(self, "someFloat", (void*)&myFloatValue); works, and myFloatValue = 2.123 but when I try double myDoubleValue; double someDo