diff --git a/mininet/node.py b/mininet/node.py
index 2c3b0c8..7e0de3f 100644
--- a/mininet/node.py
+++ b/mininet/node.py
@@ -962,7 +962,7 @@ class OVSSwitch( Switch ):
             if not intf.IP():
                 self.attach( intf )
         # Add controllers
-        clist = ','.join( [ 'tcp:%s:%d' % ( c.IP(), c.port )
+        clist = ' '.join( [ 'tcp:%s:%d' % ( c.IP(), c.port )
                             for c in controllers ] )
         self.cmd( 'ovs-vsctl set-controller', self, clist )