So the code to change the number of arguments is fine. What's wrong is the code to store the error code. That comes /after/ the three byte call primitive bytecode at the start of the method. So it should readxpc := self initialPC + 3."long store temp"(self at: xpc) = 129 ifTrue:[self at: xpc + 1 put: (16r40 + numArgs).self at: xpc + 3 put: (16r10 + numArgs)]Is there any solution to make it working?The above should work. But there's a much easier way