diff -r 30530f6c24bb Lib/distutils/msvc9compiler.py
--- a/Lib/distutils/msvc9compiler.py	Mon Mar 18 10:10:08 2013 -0700
+++ b/Lib/distutils/msvc9compiler.py	Mon Mar 18 15:25:05 2013 -0400
@@ -284,7 +284,8 @@
         popen.stderr.close()
 
     if len(result) != len(interesting):
-        raise ValueError(str(list(result.keys())))
+        msg = 'Unexpected result while detecting MS toolchain "{0}" vs "{1}"'
+        raise ValueError(msg.format(str(result), str(interesting)))
 
     return result