Index: libcxx/include/fstream
===================================================================
--- libcxx/include/fstream
+++ libcxx/include/fstream
@@ -1188,7 +1188,7 @@
     }
 #endif // _LIBCPP_STD_VER >= 17
 
-    _LIBCPP_INLINE_VISIBILITY
+    inline _LIBCPP_INLINE_VISIBILITY
     void __open(int __fd, ios_base::openmode __mode);
 #endif
     _LIBCPP_INLINE_VISIBILITY
@@ -1326,6 +1326,7 @@
 }
 
 template <class _CharT, class _Traits>
+inline _LIBCPP_INLINE_VISIBILITY
 void basic_ifstream<_CharT, _Traits>::__open(int __fd,
                                              ios_base::openmode __mode) {
   if (__sb_.__open(__fd, __mode | ios_base::in))
@@ -1401,7 +1402,7 @@
     { return open(__p.c_str(), __mode); }
 #endif // _LIBCPP_STD_VER >= 17
 
-    _LIBCPP_INLINE_VISIBILITY
+    inline _LIBCPP_INLINE_VISIBILITY
     void __open(int __fd, ios_base::openmode __mode);
 #endif
     _LIBCPP_INLINE_VISIBILITY
@@ -1539,6 +1540,7 @@
 }
 
 template <class _CharT, class _Traits>
+inline _LIBCPP_INLINE_VISIBILITY
 void basic_ofstream<_CharT, _Traits>::__open(int __fd,
                                              ios_base::openmode __mode) {
   if (__sb_.__open(__fd, __mode | ios_base::out))