diff --git a/Annex/Direct.hs b/Annex/Direct.hs
index 5724d11621..e5c1c47c82 100644
--- a/Annex/Direct.hs
+++ b/Annex/Direct.hs
@@ -441,7 +441,7 @@ setDirect wantdirect = do
  - this way things that show HEAD (eg shell prompts) will
  - hopefully show just "master". -}
 directBranch :: Ref -> Ref
-directBranch orighead = case split "/" $ fromRef orighead of
+directBranch orighead = case splitc '/' $ fromRef orighead of
 	("refs":"heads":"annex":"direct":_) -> orighead
 	("refs":"heads":rest) ->
 		Ref $ "refs/heads/annex/direct/" ++ intercalate "/" rest
@@ -452,7 +452,7 @@ directBranch orighead = case split "/" $ fromRef orighead of
  - Any other ref is left unchanged.
  -}
 fromDirectBranch :: Ref -> Ref
-fromDirectBranch directhead = case split "/" $ fromRef directhead of
+fromDirectBranch directhead = case splitc '/' $ fromRef directhead of
 	("refs":"heads":"annex":"direct":rest) -> 
 		Ref $ "refs/heads/" ++ intercalate "/" rest
 	_ -> directhead
diff --git a/Annex/TaggedPush.hs b/Annex/TaggedPush.hs
index ef1aeeea2d..3b06170b31 100644
--- a/Annex/TaggedPush.hs
+++ b/Annex/TaggedPush.hs
@@ -39,7 +39,7 @@ toTaggedBranch u info b = Git.Ref $ intercalate "/" $ catMaybes
 	]
 
 fromTaggedBranch :: Git.Branch -> Maybe (UUID, Maybe String)
-fromTaggedBranch b = case split "/" $ Git.fromRef b of
+fromTaggedBranch b = case splitc '/' $ Git.fromRef b of
 	("refs":"synced":u:info:_base) ->
 		Just (toUUID u, fromB64Maybe info)
 	("refs":"synced":u:_base) ->
diff --git a/Assistant/Ssh.hs b/Assistant/Ssh.hs
index 66ed542570..e439ecd231 100644
--- a/Assistant/Ssh.hs
+++ b/Assistant/Ssh.hs
@@ -383,7 +383,7 @@ mangleSshHostName sshdata = intercalate "-"
 
 {- Extracts the real hostname from a mangled ssh hostname. -}
 unMangleSshHostName :: String -> String
-unMangleSshHostName h = case split "-" h of
+unMangleSshHostName h = case splitc '-' h of
 	("git":"annex":rest) -> unescape (intercalate "-" (beginning rest))
 	_ -> h
   where
diff --git a/Backend/Hash.hs b/Backend/Hash.hs
index ba8d4bc641..c85047d517 100644
--- a/Backend/Hash.hs
+++ b/Backend/Hash.hs
@@ -103,7 +103,7 @@ selectExtension f
 	es = filter (not . null) $ reverse $
 		take 2 $ map (filter validInExtension) $
 		takeWhile shortenough $
-		reverse $ split "." $ takeExtensions f
+		reverse $ splitc '.' $ takeExtensions f
 	shortenough e = length e <= 4 -- long enough for "jpeg"
 
 {- A key's checksum is checked during fsck. -}
diff --git a/Build/OSXMkLibs.hs b/Build/OSXMkLibs.hs
index 948b0d5a35..2243c6b862 100644
--- a/Build/OSXMkLibs.hs
+++ b/Build/OSXMkLibs.hs
@@ -95,7 +95,7 @@ findLibPath l = go =<< getEnv "DYLD_LIBRARY_PATH"
   where
 	go Nothing = return l
 	go (Just p) = fromMaybe l
-		<$> firstM doesFileExist (map (</> f) (split ":" p))
+		<$> firstM doesFileExist (map (</> f) (splitc ':' p))
 	f = takeFileName l
 
 {- Expands any @rpath in the list of libraries.
diff --git a/CHANGELOG b/CHANGELOG
index 30b7b147b8..634b22082f 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -8,6 +8,7 @@ git-annex (6.20170102) UNRELEASED; urgency=medium
   * vicfg: Include the numcopies configuation.
   * config: New command for storing configuration in the git-annex branch.
   * stack.yaml: Update to lts-7.18.
+  * Some optimisations to string splitting code.
 
  -- Joey Hess <id@joeyh.name>  Fri, 06 Jan 2017 15:22:06 -0400
 
diff --git a/Command/AddUrl.hs b/Command/AddUrl.hs
index 8cc1484406..169875f4bf 100644
--- a/Command/AddUrl.hs
+++ b/Command/AddUrl.hs
@@ -387,7 +387,7 @@ url2file url pathdepth pathmax = case pathdepth of
 		]
 	frombits a = intercalate "/" $ a urlbits
 	urlbits = map (truncateFilePath pathmax . sanitizeFilePath) $
-		filter (not . null) $ split "/" fullurl
+		filter (not . null) $ splitc '/' fullurl
 
 urlString2file :: URLString -> Maybe Int -> Int -> FilePath
 urlString2file s pathdepth pathmax = case Url.parseURIRelaxed s of
diff --git a/Command/Map.hs b/Command/Map.hs
index 43c00d2572..b04beb477c 100644
--- a/Command/Map.hs
+++ b/Command/Map.hs
@@ -92,7 +92,7 @@ hostname r
 	| otherwise = "localhost"
 
 basehostname :: Git.Repo -> String
-basehostname r = fromMaybe "" $ headMaybe $ split "." $ hostname r
+basehostname r = fromMaybe "" $ headMaybe $ splitc '.' $ hostname r
 
 {- A name to display for a repo. Uses the name from uuid.log if available,
  - or the remote name if not. -}
diff --git a/Command/Unused.hs b/Command/Unused.hs
index 1711fe047c..3953f44861 100644
--- a/Command/Unused.hs
+++ b/Command/Unused.hs
@@ -269,7 +269,7 @@ withKeysReferencedDiff a getdiff extractsha = do
 	forM_ ds go
 	liftIO $ void clean
   where
-	go d = do
+  	go d = do
 		let sha = extractsha d
 		unless (sha == nullSha) $
 			(parseLinkOrPointer <$> catObject sha)
diff --git a/Crypto.hs b/Crypto.hs
index d3cbfa2f7f..dc1d2e6d24 100644
--- a/Crypto.hs
+++ b/Crypto.hs
@@ -231,8 +231,8 @@ instance LensGpgEncParams (RemoteConfig, RemoteGitConfig) where
  		{- When the remote is configured to use public-key encryption,
 		 - look up the recipient keys and add them to the option list. -}
 		case M.lookup "encryption" c of
-			Just "pubkey" -> Gpg.pkEncTo $ maybe [] (split ",") $ M.lookup "cipherkeys" c
-			Just "sharedpubkey" -> Gpg.pkEncTo $ maybe [] (split ",") $ M.lookup "pubkeys" c
+			Just "pubkey" -> Gpg.pkEncTo $ maybe [] (splitc ',') $ M.lookup "cipherkeys" c
+			Just "sharedpubkey" -> Gpg.pkEncTo $ maybe [] (splitc ',') $ M.lookup "pubkeys" c
 			_ -> []
 	getGpgDecParams (_c,gc) = map Param (remoteAnnexGnupgDecryptOptions gc)
 
diff --git a/Git/Command.hs b/Git/Command.hs
index adea7622e0..f40dfabcd8 100644
--- a/Git/Command.hs
+++ b/Git/Command.hs
@@ -91,16 +91,16 @@ pipeWrite params repo = withHandle StdinHandle createProcessSuccess $
 pipeNullSplit :: [CommandParam] -> Repo -> IO ([String], IO Bool)
 pipeNullSplit params repo = do
 	(s, cleanup) <- pipeReadLazy params repo
-	return (filter (not . null) $ split sep s, cleanup)
+	return (filter (not . null) $ splitc sep s, cleanup)
   where
-	sep = "\0"
+	sep = '\0'
 
 pipeNullSplitStrict :: [CommandParam] -> Repo -> IO [String]
 pipeNullSplitStrict params repo = do
 	s <- pipeReadStrict params repo
-	return $ filter (not . null) $ split sep s
+	return $ filter (not . null) $ splitc sep s
   where
-	sep = "\0"
+	sep = '\0'
 
 pipeNullSplitZombie :: [CommandParam] -> Repo -> IO [String]
 pipeNullSplitZombie params repo = leaveZombie <$> pipeNullSplit params repo
diff --git a/Git/Config.hs b/Git/Config.hs
index 65bd9b7ba3..9b4c342a4b 100644
--- a/Git/Config.hs
+++ b/Git/Config.hs
@@ -132,7 +132,7 @@ parse s
 	-- --list output will have an = in the first line
 	| all ('=' `elem`) (take 1 ls) = sep '=' ls
 	-- --null --list output separates keys from values with newlines
-	| otherwise = sep '\n' $ split "\0" s
+	| otherwise = sep '\n' $ splitc '\0' s
   where
 	ls = lines s
 	sep c = M.fromListWith (++) . map (\(k,v) -> (k, [v])) .
diff --git a/Git/Construct.hs b/Git/Construct.hs
index 765562212e..4899278805 100644
--- a/Git/Construct.hs
+++ b/Git/Construct.hs
@@ -26,7 +26,7 @@ module Git.Construct (
 #ifndef mingw32_HOST_OS
 import System.Posix.User
 #endif
-import qualified Data.Map as M hiding (map, split)
+import qualified Data.Map as M
 import Network.URI
 
 import Common
@@ -143,7 +143,7 @@ remoteNamedFromKey :: String -> IO Repo -> IO Repo
 remoteNamedFromKey k = remoteNamed basename
   where
 	basename = intercalate "." $ 
-		reverse $ drop 1 $ reverse $ drop 1 $ split "." k
+		reverse $ drop 1 $ reverse $ drop 1 $ splitc '.' k
 
 {- Constructs a new Repo for one of a Repo's remotes using a given
  - location (ie, an url). -}
diff --git a/Git/Ref.hs b/Git/Ref.hs
index 5b3b85324c..2d80137387 100644
--- a/Git/Ref.hs
+++ b/Git/Ref.hs
@@ -144,6 +144,6 @@ legal allowonelevel s = all (== False) illegal
 	ends v = v `isSuffixOf` s
 	begins v = v `isPrefixOf` s
 
-	pathbits = split "/" s
+	pathbits = splitc '/' s
 	illegalchars = " ~^:?*[\\" ++ controlchars
 	controlchars = chr 0o177 : [chr 0 .. chr (0o40-1)]
diff --git a/Limit.hs b/Limit.hs
index efe4fea85b..7b26f9e588 100644
--- a/Limit.hs
+++ b/Limit.hs
@@ -161,7 +161,7 @@ addCopies :: String -> Annex ()
 addCopies = addLimit . limitCopies
 
 limitCopies :: MkLimit Annex
-limitCopies want = case split ":" want of
+limitCopies want = case splitc ':' want of
 	[v, n] -> case parsetrustspec v of
 		Just checker -> go n $ checktrust checker
 		Nothing -> go n $ checkgroup v
diff --git a/Logs/Transfer.hs b/Logs/Transfer.hs
index 28f7b0a263..903db96fe4 100644
--- a/Logs/Transfer.hs
+++ b/Logs/Transfer.hs
@@ -268,7 +268,7 @@ readTransferInfo mpid s = TransferInfo
 	filename
 		| end rest == "\n" = beginning rest
 		| otherwise = rest
-	bits = split " " firstline
+	bits = splitc ' ' firstline
 	numbits = length bits
 	time = if numbits > 0
 		then Just <$> parsePOSIXTime =<< headMaybe bits
diff --git a/Logs/UUID.hs b/Logs/UUID.hs
index 60c8a2ef95..4c84d10bd8 100644
--- a/Logs/UUID.hs
+++ b/Logs/UUID.hs
@@ -66,7 +66,7 @@ fixBadUUID = M.fromList . map fixup . M.toList
 	newertime (LogEntry (Date d) _) = d + minimumPOSIXTimeSlice
 	newertime (LogEntry Unknown _) = minimumPOSIXTimeSlice
 	minimumPOSIXTimeSlice = 0.000001
-	isuuid s = length s == 36 && length (split "-" s) == 5
+	isuuid s = length s == 36 && length (splitc '-' s) == 5
 
 {- Records the uuid in the log, if it's not already there. -}
 recordUUID :: UUID -> Annex ()
diff --git a/Remote.hs b/Remote.hs
index 9479e72d1b..8c774915a8 100644
--- a/Remote.hs
+++ b/Remote.hs
@@ -140,7 +140,7 @@ byName' n = go . filter matching <$> remoteList
 byNameOrGroup :: RemoteName -> Annex [Remote]
 byNameOrGroup n = go =<< getConfigMaybe (ConfigKey ("remotes." ++ n))
   where
-	go (Just l) = catMaybes <$> mapM (byName . Just) (split " " l)
+	go (Just l) = catMaybes <$> mapM (byName . Just) (splitc ' ' l)
 	go Nothing = maybeToList <$> byName (Just n)
 
 {- Only matches remote name, not UUID -}
diff --git a/Remote/BitTorrent.hs b/Remote/BitTorrent.hs
index 0ec78aa642..2f29f5baa4 100644
--- a/Remote/BitTorrent.hs
+++ b/Remote/BitTorrent.hs
@@ -302,7 +302,7 @@ ariaProgress (Just sz) meter ps = do
 		=<< ariaParams ps
 
 parseAriaProgress :: Integer -> ProgressParser
-parseAriaProgress totalsize = go [] . reverse . split ['\r']
+parseAriaProgress totalsize = go [] . reverse . splitc '\r'
   where
 	go remainder [] = (Nothing, remainder)
 	go remainder (x:xs) = case readish (findpercent x) of
diff --git a/Remote/Bup.hs b/Remote/Bup.hs
index 332e8d5dc6..75b3795587 100644
--- a/Remote/Bup.hs
+++ b/Remote/Bup.hs
@@ -254,7 +254,7 @@ bup2GitRemote r
 			else giveup "please specify an absolute path"
 	| otherwise = Git.Construct.fromUrl $ "ssh://" ++ host ++ slash dir
   where
-	bits = split ":" r
+	bits = splitc ':' r
 	host = Prelude.head bits
 	dir = intercalate ":" $ drop 1 bits
 	-- "host:~user/dir" is not supported specially by bup;
diff --git a/Remote/Helper/Encryptable.hs b/Remote/Helper/Encryptable.hs
index 45ceae0681..029ac4b09c 100644
--- a/Remote/Helper/Encryptable.hs
+++ b/Remote/Helper/Encryptable.hs
@@ -165,7 +165,7 @@ extractCipher c = case (M.lookup "cipher" c,
 		Just $ SharedCipher (fromB64bs t)
 	_ -> Nothing
   where
-	readkeys = KeyIds . split ","
+	readkeys = KeyIds . splitc ','
 
 describeEncryption :: RemoteConfig -> String
 describeEncryption c = case extractCipher c of
diff --git a/Types/RefSpec.hs b/Types/RefSpec.hs
index 091631abd5..c71e57d92e 100644
--- a/Types/RefSpec.hs
+++ b/Types/RefSpec.hs
@@ -25,7 +25,7 @@ allRefSpec :: RefSpec
 allRefSpec = [AddMatching $ compileGlob "*" CaseSensative]
 
 parseRefSpec :: String -> Either String RefSpec
-parseRefSpec v = case partitionEithers (map mk $ split ":" v) of
+parseRefSpec v = case partitionEithers (map mk $ splitc ':' v) of
 	([],refspec) -> Right refspec
 	(e:_,_) -> Left e
   where
diff --git a/Upgrade/V1.hs b/Upgrade/V1.hs
index c82cf92f51..725bb40898 100644
--- a/Upgrade/V1.hs
+++ b/Upgrade/V1.hs
@@ -148,7 +148,7 @@ readKey1 v
 		, keyMtime = t
 		}
   where
-	bits = split ":" v
+	bits = splitc ':' v
 	b = Prelude.head bits
 	n = intercalate ":" $ drop (if wormy then 3 else 1) bits
 	t = if wormy
diff --git a/Utility/DottedVersion.hs b/Utility/DottedVersion.hs
index ebf4c0bd1d..3198b1ce27 100644
--- a/Utility/DottedVersion.hs
+++ b/Utility/DottedVersion.hs
@@ -25,7 +25,7 @@ instance Show DottedVersion where
 normalize :: String -> DottedVersion
 normalize v = DottedVersion v $ 
 	sum $ mult 1 $ reverse $ extend precision $ take precision $
-		map readi $ split "." v
+		map readi $ splitc '.' v
   where
 	extend n l = l ++ replicate (n - length l) 0
 	mult _ [] = []
diff --git a/Utility/Gpg.hs b/Utility/Gpg.hs
index 1185152220..a5d3820832 100644
--- a/Utility/Gpg.hs
+++ b/Utility/Gpg.hs
@@ -162,7 +162,7 @@ findPubKeys :: GpgCmd -> String -> IO KeyIds
 findPubKeys cmd for = KeyIds . parse . lines <$> readStrict cmd params
   where
 	params = [Param "--with-colons", Param "--list-public-keys", Param for]
-	parse = mapMaybe (keyIdField . split ":")
+	parse = mapMaybe (keyIdField . splitc ':')
 	keyIdField ("pub":_:_:_:f:_) = Just f
 	keyIdField _ = Nothing
 
@@ -175,7 +175,7 @@ secretKeys cmd = catchDefaultIO M.empty makemap
   where
 	makemap = M.fromList . parse . lines <$> readStrict cmd params
 	params = [Param "--with-colons", Param "--list-secret-keys", Param "--fixed-list-mode"]
-	parse = extract [] Nothing . map (split ":")
+	parse = extract [] Nothing . map (splitc ':')
 	extract c (Just keyid) (("uid":_:_:_:_:_:_:_:_:userid:_):rest) =
 		extract ((keyid, decode_c userid):c) Nothing rest
 	extract c (Just keyid) rest@(("sec":_):_) =
diff --git a/Utility/Lsof.hs b/Utility/Lsof.hs
index 27d34b5925..e3ed709ec3 100644
--- a/Utility/Lsof.hs
+++ b/Utility/Lsof.hs
@@ -107,7 +107,7 @@ parseFormatted s = bundle $ go [] $ lines s
 	parsemode ('u':_) = OpenReadWrite
 	parsemode _ = OpenUnknown
 
-	splitnull = split "\0"
+	splitnull = splitc '\0'
 
 	parsefail = error $ "failed to parse lsof output: " ++ show s
 
diff --git a/Utility/Misc.hs b/Utility/Misc.hs
index 4498c0a03e..564935ddb6 100644
--- a/Utility/Misc.hs
+++ b/Utility/Misc.hs
@@ -45,6 +45,14 @@ separate c l = unbreak $ break c l
 		| null b = r
 		| otherwise = (a, tail b)
 
+{- Split on a single character. This is over twice as fast as using
+ - Data.List.Utils.split on a list of length 1, while producing
+ - identical results. -}
+splitc :: Char -> String -> [String]
+splitc c s = case break (== c) s of
+	(i, _c:rest) -> i : splitc c rest
+	(i, []) -> i : []
+
 {- Breaks out the first line. -}
 firstLine :: String -> String
 firstLine = takeWhile (/= '\n')
diff --git a/Utility/Quvi.hs b/Utility/Quvi.hs
index d33d79bb8e..ff1ad854c5 100644
--- a/Utility/Quvi.hs
+++ b/Utility/Quvi.hs
@@ -124,14 +124,14 @@ supported Quvi09 url = (firstlevel <&&> secondlevel)
 		Nothing -> return False
 		Just auth -> do
 			let domain = map toLower $ uriRegName auth
-			let basedomain = intercalate "." $ reverse $ take 2 $ reverse $ split "." domain
+			let basedomain = intercalate "." $ reverse $ take 2 $ reverse $ splitc '.' domain
 			any (\h -> domain `isSuffixOf` h || basedomain `isSuffixOf` h) 
 				. map (map toLower) <$> listdomains Quvi09
 	secondlevel = snd <$> processTranscript "quvi"
 		(toCommand [Param "dump", Param "-o", Param url]) Nothing
 
 listdomains :: QuviVersion -> IO [String]
-listdomains Quvi09 = concatMap (split ",") 
+listdomains Quvi09 = concatMap (splitc ',') 
 	. concatMap (drop 1 . words) 
 	. filter ("domains: " `isPrefixOf`) . lines
 	<$> readQuvi (toCommand [Param "info", Param "-p", Param "domains"])
diff --git a/Utility/Rsync.hs b/Utility/Rsync.hs
index d3fe98120f..d3823a5283 100644
--- a/Utility/Rsync.hs
+++ b/Utility/Rsync.hs
@@ -24,7 +24,7 @@ rsyncShell command = [Param "-e", Param $ unwords $ map escape (toCommand comman
 	{- rsync requires some weird, non-shell like quoting in
 	- here. A doubled single quote inside the single quoted
 	- string is a single quote. -}
-	escape s = "'" ++  intercalate "''" (split "'" s) ++ "'"
+	escape s = "'" ++  intercalate "''" (splitc '\'' s) ++ "'"
 
 {- Runs rsync in server mode to send a file. -}
 rsyncServerSend :: [CommandParam] -> FilePath -> IO Bool
@@ -123,7 +123,7 @@ parseRsyncProgress = go [] . reverse . progresschunks
 	{- Find chunks that each start with delim.
 	 - The first chunk doesn't start with it
 	 - (it's empty when delim is at the start of the string). -}
-	progresschunks = drop 1 . split [delim]
+	progresschunks = drop 1 . splitc delim
 	findbytesstart s = dropWhile isSpace s
 
 	parsebytes :: String -> Maybe Integer
diff --git a/Utility/SafeCommand.hs b/Utility/SafeCommand.hs
index 5ce17a8453..bef0a619d3 100644
--- a/Utility/SafeCommand.hs
+++ b/Utility/SafeCommand.hs
@@ -11,7 +11,7 @@ module Utility.SafeCommand where
 
 import System.Exit
 import Utility.Process
-import Data.String.Utils
+import Utility.Misc
 import System.FilePath
 import Data.Char
 import Data.List
@@ -86,7 +86,7 @@ shellEscape :: String -> String
 shellEscape f = "'" ++ escaped ++ "'"
   where
 	-- replace ' with '"'"'
-	escaped = intercalate "'\"'\"'" $ split "'" f
+	escaped = intercalate "'\"'\"'" $ splitc '\'' f
 
 -- | Unescapes a set of shellEscaped words or filenames.
 shellUnEscape :: String -> [String]