diff -ru boost_1_50_0_beta1.org/tools/build/v2/tools/msvc.jam boost_1_50_0_beta1/tools/build/v2/tools/msvc.jam
--- boost_1_50_0_beta1.org/tools/build/v2/tools/msvc.jam	Thu Apr 26 03:35:55 2012
+++ boost_1_50_0_beta1/tools/build/v2/tools/msvc.jam	Tue Jun 12 08:07:02 2012
@@ -853,8 +853,11 @@
             # 'x86' when running 32-bit Windows, no matter which processor is
             # used, and 'AMD64' on 64-bit windows on x86 (either AMD64 or EM64T)
             # Windows.
+            # PROCESSOR_ARCHITEW6432 is set when running a 64-bit Windows, but
+            # the shell is 32-bit.
             #
             if [ MATCH ^(AMD64) : [ os.environ PROCESSOR_ARCHITECTURE ] ]
+                || [ MATCH ^(AMD64) : [ os.environ PROCESSOR_ARCHITEW6432 ] ]
             {
                 default-global-setup-options-amd64 = amd64 ;
             }