In a matlab gui pressing spacebar (un)checks a checkbox if it is focused. How can I turn this behaviour off?

I have a matlab gui made with guide that has a checkbox uicontroll. When that checkbox is focused, pressing spacebar (un)checks that checkbox. I don't want this behaviour - how can I turn this off?

I want to turn it off because I have defined a keypressFcn for the spacebar and I want something else to happen when the user presses the spacebar. atm that 'something else' is working. If spacebar is hit, my keypressFcn runs and does what it should do and additionally the checkbox (un)checks. I only want it to execute my keypressFcn, though..

I don't really know where to start solving this problem.. Just some generall direction instructions would already be helpfull!