diff --git a/ChangeLog b/ChangeLog
index 976cc42d04..599144ebbe 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Jul  6 21:22:16 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* cont.c (fiber_machine_stack_alloc): use MAP_FAILED instead of -1.
+
 Wed Jul  6 21:21:05 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* cont.c (fiber_machine_stack_alloc): remove unnecessary cast.
diff --git a/cont.c b/cont.c
index e260a40053..db4d93bca5 100644
--- a/cont.c
+++ b/cont.c
@@ -537,7 +537,7 @@ fiber_machine_stack_alloc(size_t size)
 	void *page;
 	STACK_GROW_DIR_DETECTION;
 	ptr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
-	if (ptr == (VALUE*)(SIGNED_VALUE)-1) {
+	if (ptr == MAP_FAILED) {
 	    rb_raise(rb_eFiberError, "can't alloc machine stack to fiber");
 	}
 	page = ptr + STACK_DIR_UPPER((size - RB_PAGE_SIZE) / sizeof(VALUE), 0);