diff --git a/Annex/Sim.hs b/Annex/Sim.hs
index 00742adb2b..6ac44e6664 100644
--- a/Annex/Sim.hs
+++ b/Annex/Sim.hs
@@ -19,6 +19,7 @@ import Annex (Annex)
 import Backend.Hash (genTestKey)
 import Annex.UUID
 import Utility.FileSystemEncoding
+import qualified Remote
 
 import System.Random
 import Data.Word
@@ -51,11 +52,12 @@ data SimState = SimState
 	, simGroupWanted :: M.Map GroupName Matcher
 	, simMaxSize :: M.Map RepoName MaxSize
 	, simRebalance :: Bool
+	, simExistingRepoByName :: ExistingRepoByName
 	}
 	deriving (Show)
 
-emptySimState :: Int -> SimState
-emptySimState rngseed = SimState
+emptySimState :: Int -> ExistingRepoByName -> SimState
+emptySimState rngseed repobyname = SimState
 	{ simRepos = mempty
 	, simSpecialRemotes = mempty
 	, simRepoState = mempty
@@ -69,6 +71,7 @@ emptySimState rngseed = SimState
 	, simGroupWanted = mempty
 	, simMaxSize = mempty
 	, simRebalance = False
+	, simExistingRepoByName = repobyname
 	}
 
 -- State that can vary between different repos in the simulation.
@@ -130,7 +133,14 @@ applySimCommand (CommandInitRemote reponame) st =
 	in Right $ st'
 		{ simSpecialRemotes = M.insert reponame u (simSpecialRemotes st')
 		}
-applySimCommand (CommandUse reponame s) st = error "TODO" -- XXX
+applySimCommand (CommandUse reponame s) st =
+	case existingRepoByName (simExistingRepoByName st) reponame of
+		(u:[], _) -> Right $ st
+			{ simSpecialRemotes = M.insert reponame u (simSpecialRemotes st)
+			}
+		(_, msg) -> Left $ "Unable to use a repository \"" 
+			++ fromRepoName reponame 
+			++ "\" in the simulation because " ++ msg
 applySimCommand (CommandConnect repo remote) st = Right $ st
 	{ simConnections = 
 		let s = case M.lookup repo (simConnections st) of
@@ -235,3 +245,15 @@ genSimUUID st (RepoName reponame) = simRandom st (randomWords 1024)
 simUUIDNameSpace :: U.UUID
 simUUIDNameSpace = U5.generateNamed U5.namespaceURL $
         B.unpack "http://git-annex.branchable.com/git-annex-sim/"
+
+newtype ExistingRepoByName = ExistingRepoByName 
+	{ existingRepoByName :: RepoName -> ([UUID], String)
+	}
+
+instance Show ExistingRepoByName where
+	show _ = "ExistingRepoByName"
+
+mkExistingRepoByName :: Annex ExistingRepoByName
+mkExistingRepoByName = do
+	f <- Remote.nameToUUID''
+	return $ ExistingRepoByName $ f . fromRepoName
diff --git a/Remote.hs b/Remote.hs
index 9e41f8ae83..0f19d7a880 100644
--- a/Remote.hs
+++ b/Remote.hs
@@ -52,6 +52,7 @@ module Remote (
 	remoteLocations,
 	nameToUUID,
 	nameToUUID',
+	nameToUUID'',
 	showTriedRemotes,
 	listRemoteNames,
 	showLocations,
@@ -148,8 +149,11 @@ byNameWithUUID = checkuuid <=< byName
 		| otherwise = return $ Just r
 
 byName' :: RemoteName -> Annex (Either String Remote)
-byName' "" = return $ Left "no repository name specified"
-byName' n = go . filter matching <$> remoteList
+byName' n = byName'' n <$> remoteList
+
+byName'' :: RemoteName -> [Remote] -> Either String Remote
+byName'' "" _ = Left "no repository name specified"
+byName'' n remotelist = go $ filter matching remotelist
   where
 	go [] = Left $ "there is no available git remote named \"" ++ n ++ "\""
 	go (match:_) = Right match
@@ -182,20 +186,31 @@ nameToUUID n = nameToUUID' n >>= \case
 	(_, msg) -> giveup msg
 
 nameToUUID' :: RemoteName -> Annex ([UUID], String)
-nameToUUID' n
+nameToUUID' n = do
+	f <- nameToUUID''
+	return (f n)
+
+nameToUUID'' :: Annex (RemoteName -> ([UUID], String))
+nameToUUID'' = do
+	l <- remoteList
+	u <- getUUID
+	m <- uuidDescMap
+	return $ \n -> nameToUUID''' n l u m
+
+nameToUUID''' :: RemoteName -> [Remote] -> UUID -> UUIDDescMap -> ([UUID], String)
+nameToUUID''' n remotelist hereu m
 	| n == "." = currentrepo
 	| n == "here" = currentrepo
-	| otherwise = byName' n >>= go
+	| otherwise = go (byName'' n remotelist)
   where
-	currentrepo = mkone <$> getUUID
+	currentrepo = mkone hereu
 
-	go (Right r) = return $ case uuid r of
+	go (Right r) = case uuid r of
 		NoUUID -> ([], noRemoteUUIDMsg r)
 		u -> mkone u
-	go (Left e) = do
-		m <- uuidDescMap
+	go (Left e) =
 		let descn = UUIDDesc (encodeBS n)
-		return $ case M.keys (M.filter (== descn) m) of
+		in case M.keys (M.filter (== descn) m) of
 			[] -> 
 				let u = toUUID n
 				in case M.keys (M.filterWithKey (\k _ -> k == u) m) of