Index: Lib/distutils/msvccompiler.py
===================================================================
--- Lib/distutils/msvccompiler.py	(revision 54501)
+++ Lib/distutils/msvccompiler.py	(working copy)
@@ -270,6 +270,12 @@
                 self.__paths.append(p)
         except KeyError:
             pass
+        reduced_paths = []
+        for p in self.__paths:
+            np = os.path.normpath(p)
+            if np not in reduced_paths:
+                reduced_paths.append(np)
+        self.__paths = reduced_paths
         os.environ['path'] = string.join(self.__paths, ';')
 
         self.preprocess_options = None