diff --git a/include/boost/config/platform/macos.hpp b/include/boost/config/platform/macos.hpp
index a172a2d1..d6877d31 100644
--- a/include/boost/config/platform/macos.hpp
+++ b/include/boost/config/platform/macos.hpp
@@ -53,10 +53,14 @@
 
 // We will eventually support threads in non-Carbon builds, but we do
 // not support this yet.
-#  if TARGET_CARBON
+#  if ( defined(TARGET_API_MAC_CARBON) && TARGET_API_MAC_CARBON ) || ( defined(TARGET_CARBON) && TARGET_CARBON )
 
 #  if !defined(BOOST_HAS_PTHREADS)
 #    define BOOST_HAS_MPTASKS
+#  elif ( __dest_os == __mac_os_x )
+// We are doing a Carbon/Mach-O/MSL build which has pthreads, but only the
+// gettimeofday and no posix.
+#  define BOOST_HAS_GETTIMEOFDAY
 #  endif
 
 // The MP task implementation of Boost Threads aims to replace MP-unsafe