diff --git a/ChangeLog b/ChangeLog
index 263b39eaff..2c9dd6154d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Jun 21 18:32:37 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ruby_atomic.h (ATOMIC_PTR_CAS): define by generic CAS macro, not
+	  via size_t, to suppress a warning by mingw gcc.
+
 Sun Jun 21 05:31:41 2015  Shota Fukumori  <her@sorah.jp>
 
 	* ext/objspace/objspace_dump.c(dump_object): Return empty JSON object when
diff --git a/ruby_atomic.h b/ruby_atomic.h
index e2b1c87a2f..ad7d77ad55 100644
--- a/ruby_atomic.h
+++ b/ruby_atomic.h
@@ -18,6 +18,7 @@ typedef unsigned int rb_atomic_t;
 # define ATOMIC_SIZE_SUB(var, val) __atomic_fetch_sub(&(var), (val), __ATOMIC_SEQ_CST)
 
 # define ATOMIC_PTR_EXCHANGE(var, val) __atomic_exchange_n(&(var), (val), __ATOMIC_SEQ_CST)
+# define ATOMIC_PTR_CAS(var, oldval, newval) ATOMIC_CAS(var, oldval, newval)
 
 #elif defined HAVE_GCC_SYNC_BUILTINS
 /* @shyouhei hack to support atomic operations in case of gcc. Gcc
@@ -36,6 +37,7 @@ typedef unsigned int rb_atomic_t; /* Anything OK */
 # define ATOMIC_SIZE_SUB(var, val) __sync_fetch_and_sub(&(var), (val))
 
 # define ATOMIC_PTR_EXCHANGE(var, val) __sync_lock_test_and_set(&(var), (val))
+# define ATOMIC_PTR_CAS(var, oldval, newval) ATOMIC_CAS(var, oldval, newval)
 
 #elif defined _WIN32
 #if defined _MSC_VER && _MSC_VER > 1200