diff --git a/a6/src/SPC.hs b/a6/src/SPC.hs
index bbfd428..1d4faf3 100644
--- a/a6/src/SPC.hs
+++ b/a6/src/SPC.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE InstanceSigs #-}
 module SPC
   ( -- * SPC startup
     SPC,
@@ -93,7 +94,7 @@ type WorkerName = String
 
 -- | Messages sent to workers. These are sent both by SPC and by
 -- processes spawned by the workes.
-data WorkerMsg 
+data WorkerMsg
   = -- | New job time
     MsgStartJob SPC (IO ()) JobId
 
@@ -129,7 +130,6 @@ data SPCState = SPCState
     spcJobsDone :: [(JobId, JobDoneReason)],
     spcJobCounter :: JobId,
     spcWorkers :: [(WorkerName, Worker)]
-    -- TODO: you will need to add more fields.
   }
 
 -- | The monad in which the main SPC thread runs. This is a state
@@ -137,6 +137,7 @@ data SPCState = SPCState
 newtype SPCM a = SPCM (SPCState -> IO (a, SPCState))
 
 instance Functor SPCM where
+  fmap :: (a -> b) -> SPCM a -> SPCM b
   fmap = liftM
 
 instance Applicative SPCM where
@@ -213,7 +214,7 @@ handleMsg c = do
         Just _ -> True
         _ -> False
     MsgAddWorker name worker -> do
-      state <- get      
+      state <- get
       put $
         state
           { spcWorkers =
@@ -230,12 +231,14 @@ handleMsg c = do
                 spcJobsDone =
                   (jobid, Done) : spcJobsDone state
               }
+        Nothing -> pure ()
+    _ -> pure ()
 
 deleteJob :: JobId -> [(JobId, (Job, Worker))] -> [(JobId, (Job, Worker))]
 deleteJob jobid list =
   case list of
     [] -> []
-    (jid, (job, w)):l -> if (jid == jobid) then l else (jid,(job,w)):(deleteJob jobid l) 
+    (jid, (job, w)):l -> if (jid == jobid) then l else (jid,(job,w)):(deleteJob jobid l)
 
 startSPC :: IO SPC
 startSPC = do
@@ -300,7 +303,7 @@ workerLoop name c = do
     MsgStartJob (SPC sc) action jobid -> do
       action
       sendTo sc $ MsgJobDone jobid
-  
+
 -- | Shut down a running worker. No effect if the worker is already
 -- terminated.
 workerStop :: Worker -> IO ()
diff --git a/a6/src/SPC_Tests.hs b/a6/src/SPC_Tests.hs
index 7976232..a55ed40 100644
--- a/a6/src/SPC_Tests.hs
+++ b/a6/src/SPC_Tests.hs
@@ -33,6 +33,6 @@ tests =
         testCase "worker-add-2-fail" $ do
           spc <- startSPC
           _ <- workerAdd spc "BD-1"
-          w <- workerAdd spc "R5-D4"
+          w <- workerAdd spc "BD-1"
           isRight w @?= False
       ]