diff --git a/include/boost/config/platform/macos.hpp b/include/boost/config/platform/macos.hpp
index 2fbea49e..dfa8eff4 100644
--- a/include/boost/config/platform/macos.hpp
+++ b/include/boost/config/platform/macos.hpp
@@ -19,7 +19,9 @@
 #    define BOOST_HAS_UNISTD_H
 #  endif
 // boilerplate code:
-#  include <boost/config/posix_features.hpp>
+#  ifndef TARGET_CARBON
+#     include <boost/config/posix_features.hpp>
+#  endif
 #  ifndef BOOST_HAS_STDINT_H
 #     define BOOST_HAS_STDINT_H
 #  endif
@@ -60,3 +62,4 @@
 #  endif
 
 #endif
+
diff --git a/include/boost/config/posix_features.hpp b/include/boost/config/posix_features.hpp
index 2d9ec29f..fad37556 100644
--- a/include/boost/config/posix_features.hpp
+++ b/include/boost/config/posix_features.hpp
@@ -31,7 +31,7 @@
       // Strictly speaking this may catch platforms with a
       // non-functioning stub <pthreads.h>, but such occurrences should
       // occur very rarely if at all.
-#     if defined(_POSIX_THREADS) && (_POSIX_THREADS+0 >= 0) && !defined(BOOST_HAS_WINTHREADS)
+#     if defined(_POSIX_THREADS) && (_POSIX_THREADS+0 >= 0) && !defined(BOOST_HAS_WINTHREADS) && !defined(BOOST_HAS_MPTASKS)
 #        define BOOST_HAS_PTHREADS
 #     endif
 
@@ -69,3 +69,4 @@
 #     endif
 
 #  endif
+