diff --git a/cli/midw.py b/cli/midw.py
index 0f973bc..7fb1397 100755
--- a/cli/midw.py
+++ b/cli/midw.py
@@ -264,7 +264,7 @@
         return
 
     for port in ports:
-        key_string = port['switch'] + "." + "%d" % port['portNumber']
+        key_string = port['switch'] + "." + "%s" % port['portNumber']
         switch_port_to_name_dict[key_string] = port['portName']
     fmtcnv.update_alias_dict("portNames", switch_port_to_name_dict)