Segfault when running "Keypad Test [Hap, 2006].ch8" rom

[kekec]

Looks like there is a segfault when running the rom mentioned below.
Debugging with GDB i can see there is a problem with the offset into the gfx array:

Program received signal SIGSEGV, Segmentation fault.
0x00401fda in runCycle () at emu8.c:445
445 gfx[x + xline + ((y + yline) * 64)] ^= 1;
(gdb) warning: cYgFFFFFFFF 611DD6C8 0
warning: cYgstd 0x22cbef d 3