diff --git a/.travis.yml b/.travis.yml
index c186d59a..9692e361 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -217,7 +217,7 @@ matrix:
 
     - os: linux
       compiler: clang++-libc++
-      env: TOOLSET=clang COMPILER="clang++-6.0 -stdlib=libc++" CXXSTD=03,11,14,1z
+      env: TOOLSET=clang COMPILER="clang++-6.0 -stdlib=libc++" CXXSTD=03,11,14
       addons:
         apt:
           packages:
diff --git a/include/boost/config/stdlib/libcpp.hpp b/include/boost/config/stdlib/libcpp.hpp
index b6a5bcf8..ffb9c1e4 100644
--- a/include/boost/config/stdlib/libcpp.hpp
+++ b/include/boost/config/stdlib/libcpp.hpp
@@ -135,4 +135,8 @@
 #  define BOOST_NO_CXX14_HDR_SHARED_MUTEX
 #endif
 
+#if !defined(BOOST_NO_CXX14_HDR_SHARED_MUTEX) && (_LIBCPP_VERSION < 5000)
+#  define BOOST_NO_CXX14_HDR_SHARED_MUTEX
+#endif
+
 //  --- end ---