diff --git a/Main.hs b/Main.hs
index 41e2032..8fd6a27 100644
--- a/Main.hs
+++ b/Main.hs
@@ -244,7 +244,7 @@ fsTreeFromDir path dir ignored = FSDir dir <$> catMaybes <$> (mapM fstreefy =<<
           then return Nothing else do
           st <- getFileStatus (path </> dir </> name)
           case st of
-            _ | isRegularFile st || isSymbolicLink st -> return $ Just $ FSFile name
+            _ | isRegularFile st || Posix.isSymbolicLink st -> return $ Just $ FSFile name
             _ | isDirectory st -> Just <$> fsTreeFromDir (path </> dir) name ignored
             _ -> return Nothing
 
@@ -442,7 +442,7 @@ main = do
             s <- getFileStatus path
             (blob, mod) <- case s of
               _ | isRegularFile s  -> (, bool 0o100755 0o100644 (fileMode s `testBit` 6)) <$> BL.readFile path
-              _ | isSymbolicLink s -> (, 0o120000) <$> BLU.fromString <$> Posix.readSymbolicLink path
+              _ | Posix.isSymbolicLink s -> (, 0o120000) <$> BLU.fromString <$> Posix.readSymbolicLink path
               _ -> error ("not a valid file to add: " ++ rpath)
             sha <- writeBlob gitdir idxmaps "blob" blob
             let fname = PF.makeRelative workdir path
diff --git a/stack.yaml b/stack.yaml
index 1a54df0..afcff19 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,4 +1,4 @@
-resolver: lts-5.15
+resolver: lts-12.7
 packages:
 - '.'
 extra-deps: []