testfor is not working in command block with comparator

Command block stopped working after upgrade to 13w39a. It was set with a testfor on a hopper clock. I checked it out and it has an error in the previous output box. It says that testfor requires a command block with analog output. But I still have the comparator connected and this was working previously.

I tried setting it up again and it won't work anymore, just gives error about analog output. It seems like it doesn't detect the comparator next to it.