diff --git a/ChangeLog b/ChangeLog
index 727c2f5811..b7bed58699 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Sat Dec  5 09:25:41 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ruby_atomic.h (ATOMIC_SIZE_CAS): fix the argument order of
+	  InterlockedCompareExchange64.  new value and then old value is
+	  the last.
+
 Sat Dec  5 09:23:34 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* random.c (fill_random_seed): fix the size to be filled, not the
diff --git a/ruby_atomic.h b/ruby_atomic.h
index 57368a7448..c8c84ed449 100644
--- a/ruby_atomic.h
+++ b/ruby_atomic.h
@@ -81,7 +81,7 @@ rb_w32_atomic_cas(volatile rb_atomic_t *var, rb_atomic_t oldval, rb_atomic_t new
 #  define ATOMIC_SIZE_INC(var) InterlockedIncrement64(&(var))
 #  define ATOMIC_SIZE_DEC(var) InterlockedDecrement64(&(var))
 #  define ATOMIC_SIZE_EXCHANGE(var, val) InterlockedExchange64(&(var), (val))
-#  define ATOMIC_SIZE_CAS(var, oldval, val) InterlockedCompareExchange64(&(var), (oldval), (val))
+#  define ATOMIC_SIZE_CAS(var, oldval, newval) InterlockedCompareExchange64(&(var), (newval), (oldval))
 # else
 #  define ATOMIC_SIZE_ADD(var, val) InterlockedExchangeAdd((LONG *)&(var), (val))
 #  define ATOMIC_SIZE_SUB(var, val) InterlockedExchangeAdd((LONG *)&(var), -(LONG)(val))