diff --git a/ChangeLog b/ChangeLog
index 2601f0e3d5..a7d903f4b5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Fri Jun 29 21:19:36 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* eval.c (stack_extend): prevent ALLOCA_N, which reserves a memory
+	  space with for restoring machine stack stored in each threads, from
+	  optimization out.  backport r34278 from the trunk.
+
 Mon May 21 16:29:47 2012  Akinori MUSHA  <knu@iDaemons.org>
 
 	* ext/syslog/syslog.c (mSyslog_inspect): Make sure self is a
diff --git a/eval.c b/eval.c
index 4d0990a54c..3ea45d6bc0 100644
--- a/eval.c
+++ b/eval.c
@@ -11040,6 +11040,7 @@ stack_extend(rb_thread_t th, int exit)
 	if (space > th->stk_pos) {
 # ifdef HAVE_ALLOCA
 	    sp = ALLOCA_N(VALUE, &space[0] - th->stk_pos);
+	    space[0] = *sp;
 # else
 	    stack_extend(th, exit);
 # endif
@@ -11054,6 +11055,7 @@ stack_extend(rb_thread_t th, int exit)
 	if (&space[STACK_PAD_SIZE] < th->stk_pos + th->stk_len) {
 # ifdef HAVE_ALLOCA
 	    sp = ALLOCA_N(VALUE, th->stk_pos + th->stk_len - &space[STACK_PAD_SIZE]);
+	    space[0] = *sp;
 # else
 	    stack_extend(th, exit);
 # endif