diff --git a/ChangeLog b/ChangeLog
index 3a1f2c7a6b..24d8f517ea 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu Oct 10 00:02:35 2013  Yusuke Endoh  <mame@tsg.ne.jp>
+
+	* numeric.c (fix_aref): avoid a possible undefined behavior.
+	  1L << 63 on 64-bit platform is undefined, at least, according to
+	  ISO/IEC 9899 (C99) 6.5.7.
+
 Wed Oct  9 23:57:02 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* object.c (id_for_attr): avoid inadvertent symbol creation.
diff --git a/numeric.c b/numeric.c
index 6979b21b65..83ed3e469d 100644
--- a/numeric.c
+++ b/numeric.c
@@ -3443,7 +3443,7 @@ fix_aref(VALUE fix, VALUE idx)
     i = FIX2LONG(idx);
 
     if (i < 0) return INT2FIX(0);
-    if (SIZEOF_LONG*CHAR_BIT-1 < i) {
+    if (SIZEOF_LONG*CHAR_BIT-1 <= i) {
 	if (val < 0) return INT2FIX(1);
 	return INT2FIX(0);
     }