diff --git a/ChangeLog b/ChangeLog
index 9f384fd..754d0e5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -106,6 +106,8 @@ additions).
 "private" knowledge of the data structures. This is unnecessary; the code has 
 been re-factored and no longer includes pcre2_internal.h.
 
+25. A racing condition is fixed in JIT reported by Mozilla.
+
 
 Version 10.21 12-January-2016
 -----------------------------
diff --git a/src/sljit/sljitUtils.c b/src/sljit/sljitUtils.c
index 6bd17e5..ec5c321 100644
--- a/src/sljit/sljitUtils.c
+++ b/src/sljit/sljitUtils.c
@@ -182,7 +182,10 @@ static pthread_mutex_t dev_zero_mutex = PTHREAD_MUTEX_INITIALIZER;
 static SLJIT_INLINE sljit_s32 open_dev_zero(void)
 {
 	pthread_mutex_lock(&dev_zero_mutex);
-	dev_zero = open("/dev/zero", O_RDWR);
+	/* The dev_zero might be initialized by another thread during the waiting. */
+	if (dev_zero < 0) {
+		dev_zero = open("/dev/zero", O_RDWR);
+	}
 	pthread_mutex_unlock(&dev_zero_mutex);
 	return dev_zero < 0;
 }