diff --git a/ChangeLog b/ChangeLog
index 429e91d29f..3723685849 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Nov 23 00:04:14 2008  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
+
+	* signal.c (ALT_STACK_SIZE): 4KB is not enough on Mac OS X.
+	  Uses SIGSTKSZ.
+
 Sat Nov 22 21:29:54 2008  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
 
 	* test/ruby/test_method.rb (test_default_accessiblity): test case for
diff --git a/signal.c b/signal.c
index 38dd55f885..0c98237f46 100644
--- a/signal.c
+++ b/signal.c
@@ -416,7 +416,11 @@ typedef RETSIGTYPE (*sighandler_t)(int);
 
 #ifdef POSIX_SIGNAL
 #ifdef USE_SIGALTSTACK
+#ifdef SIGSTKSZ
+#define ALT_STACK_SIZE SIGSTKSZ
+#else
 #define ALT_STACK_SIZE (4*1024)
+#endif
 /* alternate stack for SIGSEGV */
 static void register_sigaltstack() {
     stack_t newSS, oldSS;