diff --git a/ChangeLog b/ChangeLog
index bc2511a651..1dbc297e24 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Dec  2 06:02:00 2012  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* gc.h (SET_MACHINE_STACK_END): add volatile for preventing
+	  harmful optimization.
+
 Sun Dec  2 05:01:58 2012  Koichi Sasada  <ko1@atdot.net>
 
 	* iseq.c (rb_iseq_line_trace_each): iterate `line' event only.
diff --git a/gc.h b/gc.h
index 2a3dd92c01..10f634e346 100644
--- a/gc.h
+++ b/gc.h
@@ -3,9 +3,9 @@
 #define RUBY_GC_H 1
 
 #if defined(__x86_64__) && defined(__GNUC__) && !defined(__native_client__)
-#define SET_MACHINE_STACK_END(p) __asm__("movq\t%%rsp, %0" : "=r" (*(p)))
+#define SET_MACHINE_STACK_END(p) __asm__ volatile ("movq\t%%rsp, %0" : "=r" (*(p)))
 #elif defined(__i386) && defined(__GNUC__) && !defined(__native_client__)
-#define SET_MACHINE_STACK_END(p) __asm__("movl\t%%esp, %0" : "=r" (*(p)))
+#define SET_MACHINE_STACK_END(p) __asm__ volatile ("movl\t%%esp, %0" : "=r" (*(p)))
 #else
 NOINLINE(void rb_gc_set_stack_end(VALUE **stack_end_p));
 #define SET_MACHINE_STACK_END(p) rb_gc_set_stack_end(p)