diff --git a/Lib/dospath.py b/Lib/dospath.py
index 5a813d0..cb98576 100644
--- a/Lib/dospath.py
+++ b/Lib/dospath.py
@@ -107,12 +107,9 @@
 def commonprefix(m):
     "Given a list of pathnames, returns the longest common leading component"
     if not m: return ''
-    n = m[:]
+    n = map(string.lower, m)
     for i in range(len(n)):
-        n[i] = n[i].split(os.sep)
-        # if os.sep didn't have any effect, try os.altsep
-        if os.altsep and len(n[i]) == 1:
-            n[i] = n[i].split(os.altsep)
+        n[i] = re.split(r"[/\\]", n[i])
             
     prefix = n[0]
     for item in n:
@@ -121,7 +118,7 @@
                 prefix = prefix[:i]
                 if i == 0: return ''
                 break
-    return os.sep.join(prefix)
+    return "\\".join(prefix)
 
 
 # Get size, mtime, atime of files.