diff --git a/ChangeLog b/ChangeLog
index 1c4b245a9d..931ed413ba 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Oct 18 13:24:17 2015  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* random.c (fill_random_bytes_syscall): use ATOMIC_SET() for
+	  updating try_syscall.
+
 Sun Oct 18 13:03:52 2015  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* include/ruby/backward/util.h: Good-by Borland-C.
diff --git a/random.c b/random.c
index 9f39dc2268..4a9d4dec01 100644
--- a/random.c
+++ b/random.c
@@ -531,7 +531,7 @@ fill_random_bytes_syscall(void *seed, size_t size)
 	errno = 0;
 	ret = syscall(SYS_getrandom, seed, size, GRND_NONBLOCK);
 	if (errno == ENOSYS) {
-	    try_syscall = 0;
+	    ATOMIC_SET(try_syscall, 0);
 	    return -1;
 	}
 	if ((size_t)ret == size) return 0;