diff --git a/TODO.md b/TODO.md
index fcaed6a..525d202 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,7 +1,7 @@
 
 ## TODO
 
-- [ ] redo code to determine base path
+- [x] redo code to determine base path
 - [ ] save/load results of processing a module
   - [ ] keep each module separate in context
     - search would include imported modules, collect ops into and from modules
diff --git a/port/Lib/Util.newt b/port/Lib/Util.newt
index 51ffc22..ef99172 100644
--- a/port/Lib/Util.newt
+++ b/port/Lib/Util.newt
@@ -1,6 +1,7 @@
 module Lib.Util
 
 import Lib.Types
+import Data.List1
 
 
 funArgs : Tm -> (Tm × List Tm)
@@ -24,3 +25,28 @@ splitTele = go Nil
     go : List Binder -> Tm -> (Tm × List Binder)
     go ts (Pi fc nm icit quant t u) = go (MkBinder fc nm icit quant t :: ts) u
     go ts tm = (tm, reverse ts)
+
+
+
+getBaseDir : String → String → M (String × QName)
+getBaseDir fn modName = do
+  let (path, modName') = unsnoc $ split1 modName "."
+  let parts = split1 fn "/"
+  let (dirs,file) = unsnoc parts
+  let (name, ext) = splitFileName file
+
+  let parts = split1 fn "/"
+  let (dirs,file) = unsnoc parts
+  let (path, modName') = unsnoc $ split1 modName "."
+  unless (modName' == name) $ \ _ => error (MkFC fn (0,0)) "module name \{modName'} doesn't match \{name}"
+  let (Right base) = baseDir (Lin <>< dirs) (Lin <>< path)
+    | Left err => error (MkFC fn (0,0)) err
+  let base = if base == "" then "." else base
+  pure (base, QN path modName')
+  where
+    baseDir : SnocList String -> SnocList String -> Either String String
+    baseDir dirs Lin = Right $ joinBy "/" (dirs <>> Nil)
+    baseDir (dirs :< d) (ns :< n) = if d == n
+      then baseDir dirs ns
+      else Left "module path doesn't match directory"
+    baseDir Lin _ = Left "module path doesn't match directory"
diff --git a/port/Main.newt b/port/Main.newt
index c8f4e4a..870add7 100644
--- a/port/Main.newt
+++ b/port/Main.newt
@@ -165,14 +165,15 @@ processFile fn = do
   let dir = if dirs == Nil then "." else joinBy "/" dirs
   let (name, ext) = splitFileName file
   putStrLn "\{show dir} \{show name} \{show ext}"
+
   (Right src) <- liftIO {M} $ readFile fn
     | Left err => error (MkFC fn (0,0)) "error reading \{fn}: \{show err}"
   let (Right toks) = tokenise fn src
     | Left err => throwError err
   let (Right ((nameFC, modName), _, _)) = partialParse fn parseModHeader EmptyMap toks
     | Left (err,toks) => throwError err
-  let ns = split modName "."
-  let (path, modName') = unsnoc $ split1 modName "."
+
+  (base,qn) <- getBaseDir fn modName
 
   -- Any case splits after this point causes it to loop, no idea why
 
@@ -186,9 +187,8 @@ processFile fn = do
   processDecl ("Prim" :: Nil) (PType emptyFC "Int" Nothing)
   processDecl ("Prim" :: Nil) (PType emptyFC "String" Nothing)
   processDecl ("Prim" :: Nil) (PType emptyFC "Char" Nothing)
-  -- let base = "aoc2024" -- FIXME
-  let base = "port" -- FIXME
-  src <- processModule emptyFC base Nil (QN path modName')
+
+  src <- processModule emptyFC base Nil qn
   top <- get
   -- -- dumpContext top