diff --git a/mininet/clean.py b/mininet/clean.py
index ea9d81c..b48d702 100755
--- a/mininet/clean.py
+++ b/mininet/clean.py
@@ -53,9 +53,9 @@ class Cleanup( object ):
 
         info( "*** Removing excess controllers/ofprotocols/ofdatapaths/"
               "pings/noxes\n" )
-        zombies = ( 'controller ofprotocol ofdatapath ping nox_core'
-                    'lt-nox_core ovs-openflowd ovs-controller'
-                    'ovs-testcontroller udpbwtest mnexec ivs ryu-manager' )
+        zombies = ( 'controller ofprotocol ofdatapath ping nox_core '
+                    'lt-nox_core ovs-openflowd ovs-controller '
+                    'ovs-testcontroller udpbwtest mnexec ivs ryu-manager ' )
         # Note: real zombie processes can't actually be killed, since they
         # are already (un)dead. Then again,
         # you can't connect to them either, so they're mostly harmless.