Index: boost/config/stdlib/libstdcpp3.hpp
===================================================================
--- boost/config/stdlib/libstdcpp3.hpp.orig     2012-01-14 19:15:34.957877838 +0100
+++ boost/config/stdlib/libstdcpp3.hpp  2012-01-14 19:19:09.660901373 +0100
@@ -34,7 +34,8 @@
 #ifdef __GLIBCXX__ // gcc 3.4 and greater:
 #  if defined(_GLIBCXX_HAVE_GTHR_DEFAULT) \
         || defined(_GLIBCXX__PTHREADS) \
-        || defined(_GLIBCXX_HAS_GTHREADS)
+        || defined(_GLIBCXX_HAS_GTHREADS) \
+        || defined(_WIN32)
       //
       // If the std lib has thread support turned on, then turn it on in Boost
       // as well.  We do this because some gcc-3.4 std lib headers define _REENTANT