diff --git a/libcxx/include/__threading_support b/libcxx/include/__threading_support
index eaa402abae351..ccbcc652d9e50 100644
--- a/libcxx/include/__threading_support
+++ b/libcxx/include/__threading_support
@@ -102,7 +102,7 @@ typedef cnd_t __libcpp_condvar_t;
 #define _LIBCPP_CONDVAR_INITIALIZER {}
 
 // Execute once
-typedef once_flag __libcpp_exec_once_flag;
+typedef ::once_flag __libcpp_exec_once_flag;
 #define _LIBCPP_EXEC_ONCE_INITIALIZER ONCE_FLAG_INIT
 
 // Thread id