diff --git a/libc/upstream-netbsd/reentrant.h b/libc/upstream-netbsd/reentrant.h
index e2945da..3ca8fd6 100644
--- a/libc/upstream-netbsd/reentrant.h
+++ b/libc/upstream-netbsd/reentrant.h
@@ -28,6 +28,8 @@
 
 #define MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
 #define mutex_t pthread_mutex_t
+#define mutex_lock(x) pthread_mutex_lock(x)
+#define mutex_unlock(x) pthread_mutex_unlock(x)
 
 #define RWLOCK_INITIALIZER PTHREAD_RWLOCK_INITIALIZER
 #define rwlock_t pthread_rwlock_t