--- urllib.py.old	2007-02-20 18:16:34.000000000 +0100
+++ urllib.py	2007-02-20 18:16:13.000000000 +0100
@@ -866,8 +866,15 @@
         if not conn:
             # Set transfer mode to ASCII!
             self.ftp.voidcmd('TYPE A')
-            # Try a directory listing
-            if file: cmd = 'LIST ' + file
+            # Try a directory listing. Verify that directory exists.
+            if file:
+                pwd = self.ftp.pwd()
+                try:
+                    self.ftp.cwd(file)
+                except ftplib.error_perm, reason:
+                    raise IOError, reason, sys.exc_info()[2]
+                self.ftp.cwd(pwd)
+                cmd = 'LIST ' + file
             else: cmd = 'LIST'
             conn = self.ftp.ntransfercmd(cmd)
         self.busy = 1