diff --git a/include/mutex b/include/mutex
index 8526533f1..3b878c642 100644
--- a/include/mutex
+++ b/include/mutex
@@ -559,6 +559,7 @@ public:
 #endif
 
 template <class _Fp>
+inline _LIBCPP_INLINE_VISIBILITY
 void
 __call_once_proxy(void* __vp)
 {