diff --git a/include/etl/mutex/mutex_gcc_sync.h b/include/etl/mutex/mutex_gcc_sync.h
index 7e909ab1..298497c0 100644
--- a/include/etl/mutex/mutex_gcc_sync.h
+++ b/include/etl/mutex/mutex_gcc_sync.h
@@ -61,7 +61,7 @@ namespace etl
 
     bool try_lock()
     {
-      return (__sync_lock_test_and_set(&flag, 1U) == 1U);
+      return (__sync_lock_test_and_set(&flag, 1U) == 0U);
     }
 
     void unlock()