diff --git a/include/boost/config/platform/macos.hpp b/include/boost/config/platform/macos.hpp
index c19a6e6e..51d03012 100644
--- a/include/boost/config/platform/macos.hpp
+++ b/include/boost/config/platform/macos.hpp
@@ -39,5 +39,21 @@
 #    define BOOST_NO_STDC_NAMESPACE
 #  endif
 
-#endif
+#else
 
+// We will eventually support threads in non-Carbon builds, but we do
+// not support this yet.
+#  if TARGET_CARBON
+
+#    define BOOST_HAS_MPTASKS
+
+// The MP task implementation of Boost Threads aims to replace MP-unsafe
+// parts of the MSL, so we turn on threads unconditionally.
+#    define BOOST_HAS_THREADS
+
+// The remote call manager depends on this.
+#    define BOOST_BIND_ENABLE_PASCAL
+
+#  endif
+
+#endif
diff --git a/include/boost/config/suffix.hpp b/include/boost/config/suffix.hpp
index 56a15120..d0a94451 100644
--- a/include/boost/config/suffix.hpp
+++ b/include/boost/config/suffix.hpp
@@ -144,7 +144,8 @@
 // Turn threading support off if we don't recognise the threading API:
 //
 #if defined(BOOST_HAS_THREADS) && !defined(BOOST_HAS_PTHREADS)\
-      && !defined(BOOST_HAS_WINTHREADS) && !defined(BOOST_HAS_BETHREADS)
+      && !defined(BOOST_HAS_WINTHREADS) && !defined(BOOST_HAS_BETHREADS)\
+      && !defined(BOOST_HAS_MPTASKS)
 #  undef BOOST_HAS_THREADS
 #endif