diff --git a/ChangeLog b/ChangeLog
index 1a5f1284d5..149835062d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Apr 15 07:34:49 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* thread_pthread.c (reserve_stack): keep sp safe zone to get rid
+	  of crash by -fstack-check.  [ruby-core:68740] [Bug #11030]
+
 Tue Apr 14 16:03:49 2015  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* tool/merger.rb (versionup): should also increment revision when
diff --git a/thread_pthread.c b/thread_pthread.c
index 624095755a..224da92af4 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -662,11 +662,16 @@ reserve_stack(volatile char *limit, size_t size)
 # endif
     struct rlimit rl;
     volatile char buf[0x100];
+    enum {stack_check_margin = 0x1000}; /* for -fstack-check */
+
     STACK_GROW_DIR_DETECTION;
 
     if (!getrlimit(RLIMIT_STACK, &rl) && rl.rlim_cur == RLIM_INFINITY)
 	return;
 
+    if (size < stack_check_margin) return;
+    size -= stack_check_margin;
+
     size -= sizeof(buf); /* margin */
     if (IS_STACK_DIR_UPPER()) {
 	const volatile char *end = buf + sizeof(buf);
@@ -674,13 +679,14 @@ reserve_stack(volatile char *limit, size_t size)
 	if (limit > end) {
 	    size = limit - end;
 	    limit = alloca(size);
-	    limit[size-1] = 0;
+	    limit[stack_check_margin+size-1] = 0;
 	}
     }
     else {
 	limit -= size;
 	if (buf > limit) {
 	    limit = alloca(buf - limit);
+	    limit -= stack_check_margin;
 	    limit[0] = 0;
 	}
     }