diff --git a/ChangeLog b/ChangeLog
index 45ae085de9..73d38ac676 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon May 30 10:26:51 2011  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* numeric.c (int_pow): make sure to assign the result of x * z.
+	  If xz is optimized out, the value won't overflow.
+
 Sun May 29 23:17:29 2011  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* re.c (rb_reg_match): fix rdoc of Regexp#=~.
diff --git a/numeric.c b/numeric.c
index 09860dc6f2..1b80a2b6e0 100644
--- a/numeric.c
+++ b/numeric.c
@@ -2637,7 +2637,7 @@ int_pow(long x, unsigned long y)
 	    y >>= 1;
 	}
 	{
-	    long xz = x * z;
+	    volatile long xz = x * z;
 	    if (!POSFIXABLE(xz) || xz / x != z) {
 		goto bignum;
 	    }