diff --git a/ChangeLog b/ChangeLog
index 210287c3ff..8462bd171c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Jul 29 11:07:10 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* internal.h (LIKELY, UNLIKELY): make a boolean to enforce 1 or 0.
+
 Wed Jul 29 10:44:43 2015  Alex Dowad  <alexinbeijing@gmail.com>
 
 	* gc.c: document argument passed to finalizer proc.
diff --git a/internal.h b/internal.h
index 58ff89763c..a9b3ee4824 100644
--- a/internal.h
+++ b/internal.h
@@ -25,8 +25,8 @@ extern "C" {
 
 /* likely */
 #if __GNUC__ >= 3
-#define LIKELY(x)   (__builtin_expect((x), 1))
-#define UNLIKELY(x) (__builtin_expect((x), 0))
+#define LIKELY(x)   (__builtin_expect(!(x), 0))
+#define UNLIKELY(x) (__builtin_expect(!(x), 1))
 #else /* __GNUC__ >= 3 */
 #define LIKELY(x)   (x)
 #define UNLIKELY(x) (x)