diff --git a/libc/bionic/pthread_mutex.cpp b/libc/bionic/pthread_mutex.cpp
index 8eaf95fc3..11a66ab88 100644
--- a/libc/bionic/pthread_mutex.cpp
+++ b/libc/bionic/pthread_mutex.cpp
@@ -783,7 +783,7 @@ int pthread_mutex_lock_timeout_np_impl(pthread_mutex_t *mutex, unsigned msecs)
          * thread.
          */
         if (MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(mvalue)) {
-            if (__futex_wait_ex(&mutex->value, shared, mvalue, &ts) == ETIMEDOUT) {
+            if (__futex_wait_ex(&mutex->value, shared, mvalue, &ts) == (-ETIMEDOUT)) {
                 return EBUSY;
             }
             mvalue = mutex->value;