diff --git a/Command/MetaData.hs b/Command/MetaData.hs
index e0b86e5302..076fe38bb6 100644
--- a/Command/MetaData.hs
+++ b/Command/MetaData.hs
@@ -119,8 +119,9 @@ perform c o k = case getSet o of
 cleanup :: Key -> CommandCleanup
 cleanup k = do
 	m <- getCurrentMetaData k
-	let Object o = toJSON' (MetaDataFields m)
-	maybeShowJSON $ AesonObject o
+	case toJSON' (MetaDataFields m) of
+		Object o -> maybeShowJSON $ AesonObject o
+		_ -> noop
 	showLongNote $ unlines $ concatMap showmeta $
 		map unwrapmeta (fromMetaData m)
 	return True
diff --git a/Config/Cost.hs b/Config/Cost.hs
index 290b22a9c6..c7d4d378cc 100644
--- a/Config/Cost.hs
+++ b/Config/Cost.hs
@@ -46,9 +46,9 @@ insertCostAfter [] _ = []
 insertCostAfter l pos
 	| pos < 0 = costBetween 0 (l !! 0) : l
 	| nextpos > maxpos = l ++ [1 + l !! maxpos]
-	| item == nextitem =
-		let (_dup:new:l') = insertCostAfter lastsegment 0
-		in firstsegment ++ [costBetween item new, new] ++ l'
+	| item == nextitem = case insertCostAfter lastsegment 0 of
+		(_dup:new:l') -> firstsegment ++ [costBetween item new, new] ++ l'
+		_ -> error "insertCostAfter internal error"
 	| otherwise =
 		firstsegment ++ [costBetween item nextitem ] ++ lastsegment
   where
diff --git a/Git/UnionMerge.hs b/Git/UnionMerge.hs
index 2cf103dd9d..c603453340 100644
--- a/Git/UnionMerge.hs
+++ b/Git/UnionMerge.hs
@@ -84,14 +84,16 @@ doMerge hashhandle ch differ repo streamer = do
  - a line suitable for update-index that union merges the two sides of the
  - diff. -}
 mergeFile :: S.ByteString -> RawFilePath -> HashObjectHandle -> CatFileHandle -> IO (Maybe L.ByteString)
-mergeFile info file hashhandle h = case filter (`notElem` nullShas) [Ref asha, Ref bsha] of
-	[] -> return Nothing
-	(sha:[]) -> use sha
-	shas -> use
-		=<< either return (hashBlob hashhandle . L8.unlines)
-		=<< calcMerge . zip shas <$> mapM getcontents shas
+mergeFile info file hashhandle h = case S8.words info of
+	[_colonmode, _bmode, asha, bsha, _status] -> 
+		case filter (`notElem` nullShas) [Ref asha, Ref bsha] of
+		[] -> return Nothing
+		(sha:[]) -> use sha
+		shas -> use
+			=<< either return (hashBlob hashhandle . L8.unlines)
+			=<< calcMerge . zip shas <$> mapM getcontents shas
+	_ -> return Nothing
   where
-	[_colonmode, _bmode, asha, bsha, _status] = S8.words info
 	use sha = return $ Just $
 		updateIndexLine sha TreeFile $ asTopFilePath file
 	-- Get file and split into lines to union merge.
diff --git a/Logs/Transfer.hs b/Logs/Transfer.hs
index ab9a8ca61b..1b30e9548a 100644
--- a/Logs/Transfer.hs
+++ b/Logs/Transfer.hs
@@ -143,12 +143,12 @@ getTransfers' dirs wanted = do
 	transfers <- filter (wanted . transferKey)
 		<$> mapMaybe parseTransferFile . concat <$> findfiles
 	infos <- mapM checkTransfer transfers
-	return $ map (\(t, Just i) -> (t, i)) $
-		filter running $ zip transfers infos
+	return $ mapMaybe running $ zip transfers infos
   where
 	findfiles = liftIO . mapM dirContentsRecursive
 		=<< mapM (fromRepo . transferDir) dirs
-	running (_, i) = isJust i
+	running (t, Just i) = Just (t, i)
+	running (_, Nothing) = Nothing
 
 {- Number of bytes remaining to download from matching downloads that are in
  - progress. -}
diff --git a/Messages/JSON.hs b/Messages/JSON.hs
index 7561c61261..148e392c72 100644
--- a/Messages/JSON.hs
+++ b/Messages/JSON.hs
@@ -65,9 +65,11 @@ none :: JSONBuilder
 none = id
 
 start :: String -> Maybe RawFilePath -> Maybe Key -> JSONBuilder
-start command file key _ = Just (o, False)
+start command file key _ = case j of
+	Object o -> Just (o, False)
+	_ -> Nothing
   where
-	Object o = toJSON' $ JSONActionItem
+	j = toJSON' $ JSONActionItem
 		{ itemCommand = Just command
 		, itemKey = key
 		, itemFile = fromRawFilePath <$> file
@@ -102,18 +104,22 @@ note s (Just (o, e)) = Just (HM.insertWith combinelines "note" (toJSON' s) o, e)
 	combinelines new _old = new
 
 info :: String -> JSONBuilder
-info s _ = Just (o, True)
+info s _ = case j of
+	Object o -> Just (o, True)
+	_ -> Nothing
   where
-	Object o = object ["info" .= toJSON' s]
+	j = object ["info" .= toJSON' s]
 
 data JSONChunk v where
 	AesonObject :: Object -> JSONChunk Object
 	JSONChunk :: ToJSON' v => [(String, v)] -> JSONChunk [(String, v)]
 
 add :: JSONChunk v -> JSONBuilder
-add v (Just (o, e)) = Just (HM.union o' o, e)
+add v (Just (o, e)) = case j of
+	Object o' -> Just (HM.union o' o, e)
+	_ -> Nothing
   where
-	Object o' = case v of
+	j = case v of
 		AesonObject ao -> Object ao
 		JSONChunk l -> object $ map mkPair l
 	mkPair (s, d) = (packString s, toJSON' d)
@@ -125,12 +131,15 @@ complete v _ = add v (Just (HM.empty, True))
 -- Show JSON formatted progress, including the current state of the JSON 
 -- object for the action being performed.
 progress :: Maybe Object -> Maybe Integer -> BytesProcessed -> IO ()
-progress maction msize bytesprocessed = emit $ case maction of
-	Just action -> HM.insert "action" (Object action) o
-	Nothing -> o
+progress maction msize bytesprocessed = 
+	case j of
+		Object o -> emit $ case maction of
+			Just action -> HM.insert "action" (Object action) o
+			Nothing -> o
+		_ -> return ()
   where
 	n = fromBytesProcessed bytesprocessed :: Integer
-	Object o = case msize of
+	j = case msize of
 		Just size -> object
 			[ "byte-progress" .= n
 			, "percent-progress" .= showPercentage 2 (percentage size n)
diff --git a/Remote/Bup.hs b/Remote/Bup.hs
index 005a8a89f4..51c0ebd295 100644
--- a/Remote/Bup.hs
+++ b/Remote/Bup.hs
@@ -223,8 +223,10 @@ storeBupUUID u buprepo = do
 					giveup "ssh failed"
 		else liftIO $ do
 			r' <- Git.Config.read r
-			let ConfigValue olduuid = Git.Config.get configkeyUUID mempty r'
-			when (S.null olduuid) $
+			let noolduuid = case Git.Config.get configkeyUUID mempty r' of
+				ConfigValue olduuid -> S.null olduuid
+				NoConfigValue -> True
+			when noolduuid $
 				Git.Command.run
 					[ Param "config"
 					, Param "annex.uuid"