--- ruby-1.9.3-p194/gc.h
+++ ruby-1.9.3-p194/gc.h
@@ -3,7 +3,7 @@
 #define RUBY_GC_H 1
 
 #if defined(__x86_64__) && defined(__GNUC__)
-#define SET_MACHINE_STACK_END(p) __asm__("movq\t%%rsp, %0" : "=r" (*(p)))
+#define SET_MACHINE_STACK_END(p) __asm__("movq\t%%rsp, %q0" : "=r" (*(p)))
 #elif defined(__i386) && defined(__GNUC__)
 #define SET_MACHINE_STACK_END(p) __asm__("movl\t%%esp, %0" : "=r" (*(p)))
 #else