diff --git a/Lib/macpath.py b/Lib/macpath.py
index 7634f8e..15f42f2 100644
--- a/Lib/macpath.py
+++ b/Lib/macpath.py
@@ -89,29 +89,6 @@
 def basename(s): return split(s)[1]
 
 
-# Return the longest prefix of all list elements.
-# XXX completely untested on Mac!!!
-
-def commonprefix(m):
-    "Given a list of pathnames, returns the longest common leading component"
-    if not m: return ''
-    n = 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)
-            
-    prefix = n[0]
-    for item in n:
-        for i in range(len(prefix)):
-            if prefix[:i+1] <> item[:i+1]:
-                prefix = prefix[:i]
-                if i == 0: return ''
-                break
-    return os.sep.join(prefix)
-
-
 def isdir(s):
     """Return true if the pathname refers to an existing directory."""
 
@@ -166,6 +143,19 @@
         return 0
     return 1
 
+# Return the longest prefix of all list elements.
+
+def commonprefix(m):
+    "Given a list of pathnames, returns the longest common leading component"
+    if not m: return ''
+    prefix = m[0]
+    for item in m:
+        for i in range(len(prefix)):
+            if prefix[:i+1] <> item[:i+1]:
+                prefix = prefix[:i]
+                if i == 0: return ''
+                break
+    return prefix
 
 def expandvars(path):
     """Dummy to retain interface-compatibility with other operating systems."""