diff --git a/src/thread/pthread_spin_trylock.c b/src/thread/pthread_spin_trylock.c
index c12696b3010b332706d203faa7e16cad62433bca..1fc5f73c174ec890da1457bb8bd776f9e1fb3bc2 100644
--- a/src/thread/pthread_spin_trylock.c
+++ b/src/thread/pthread_spin_trylock.c
@@ -2,5 +2,6 @@
 
 int pthread_spin_trylock(pthread_spinlock_t *s)
 {
-	return -a_xchg(s, 1) & EBUSY;
+	if (*s || a_xchg(s, 1)) return EBUSY;
+	return 0;
 }