QPF opens 32 bit version of quartus 31.1.4

Hi,

when I open a QPF file by double clicking windows opens the 32bit version of Quartus.

Does anyone know how to make it open the 64 bit version be default?

I'm using Windows 7, Quartus II 13.1.4.

I've tried to tell windows to "open with..." and point to the 64bit executable but no joy.