[Haskell-cafe] Odd error message from ghc --make

I was just running a test that has compiled before just fine, and now I'm getting this rather odd message: EventBusTest.hs:20:9: Couldn't match expected type `Bus a' against inferred type `buster-1.1:App.EventBus.Bus [buster-1.1:App.EventBus.EData a1]' Expected type: MVar (Bus a) Inferred type: MVar (buster-1.1:App.EventBus.Bus [buster-1.1:App.EventBus.EData a1]) In the expression: mk In the first argument of `bus', namely `[mk]' Any ideas? I mean, it looks like it type checks to me.