diff --git a/Language/Preprocessor/Cpphs/Position.hs b/Language/Preprocessor/Cpphs/Position.hs
--- a/Language/Preprocessor/Cpphs/Position.hs
+++ b/Language/Preprocessor/Cpphs/Position.hs
@@ -17,7 +17,6 @@
   , addcol, newline, tab, newlines, newpos
   , cppline, haskline, cpp2hask
   , filename, lineno, directory
-  , cleanPath
   ) where
 
 import Data.List (isPrefixOf)
@@ -39,7 +38,7 @@
 
 -- | Constructor.  Argument is filename.
 newfile :: String -> Posn
-newfile name = Pn (cleanPath name) 1 1 Nothing
+newfile name = Pn name 1 1 Nothing
 
 -- | Increment column number by given quantity.
 addcol :: Int -> Posn -> Posn
@@ -97,10 +96,3 @@
 dirname  = reverse . safetail . dropWhile (not.(`elem`"\\/")) . reverse
   where safetail [] = []
         safetail (_:x) = x
-
--- | Sigh.  Mixing Windows filepaths with unix is bad.  Make sure there is a
---   canonical path separator.
-cleanPath :: FilePath -> FilePath
-cleanPath [] = []
-cleanPath ('\\':cs) = '/': cleanPath cs
-cleanPath (c:cs)    = c:   cleanPath cs
diff --git a/Language/Preprocessor/Cpphs/ReadFirst.hs b/Language/Preprocessor/Cpphs/ReadFirst.hs
--- a/Language/Preprocessor/Cpphs/ReadFirst.hs
+++ b/Language/Preprocessor/Cpphs/ReadFirst.hs
@@ -18,11 +18,12 @@
   ) where
 
 import System.IO
-import System.Directory (doesFileExist)
+import System.Directory (doesFileExist,findFile)
+import System.FilePath  (isRelative)
 import Data.List        (intersperse)
 import Control.Exception as E
 import Control.Monad    (when)
-import Language.Preprocessor.Cpphs.Position  (Posn,directory,cleanPath)
+import Language.Preprocessor.Cpphs.Position  (Posn,directory)
 
 -- | Attempt to read the given file from any location within the search path.
 --   The first location found is returned, together with the file content.
@@ -36,27 +37,25 @@
               , String
               )                 -- ^ discovered filepath, and file contents
 
-readFirst name demand path warn =
-    case name of
-       nm@(c:':':_) -> try nm [""]  -- Windows absolute path
-       '/':nm -> try nm   [""]
-       _      -> try name (cons dd (".":path))
+
+readFirst name demand paths warn = do
+  case (isRelative name, directory demand) of
+    (False, _) -> try name []
+    (_, "") -> try name (".":paths)
+    (_, dd) -> try name (dd:".":paths)
   where
-    dd = directory demand
-    cons x xs = if null x then xs else x:xs
-    try name [] = do
-        when warn $
+    try name ds = do
+      file <- findFile ds name
+      case file of
+        Just f -> do
+          content <- readFileUTF8 f
+          return (f,content)
+        Nothing -> do
           hPutStrLn stderr ("Warning: Can't find file \""++name
                            ++"\" in directories\n\t"
-                           ++concat (intersperse "\n\t" (cons dd (".":path)))
+                           ++concat (intersperse "\n\t" ds)
                            ++"\n  Asked for by: "++show demand)
-        return ("missing file: "++name,"")
-    try name (p:ps) = do
-        let file = cleanPath p++'/':cleanPath name
-        ok <- doesFileExist file
-        if not ok then try name ps
-          else do content <- readFileUTF8 file
-                  return (file,content)
+          return ("missing file: "++name,"")
 
 readFileUTF8 :: FilePath -> IO String
 readFileUTF8 file = do
diff --git a/Language/Preprocessor/Cpphs/RunCpphs.hs b/Language/Preprocessor/Cpphs/RunCpphs.hs
--- a/Language/Preprocessor/Cpphs/RunCpphs.hs
+++ b/Language/Preprocessor/Cpphs/RunCpphs.hs
@@ -15,7 +15,7 @@
 import Language.Preprocessor.Cpphs.Options  (CpphsOptions(..), BoolOptions(..)
                                             ,trailing)
 import Language.Preprocessor.Cpphs.Tokenise (deWordStyle, tokenise)
-import Language.Preprocessor.Cpphs.Position (cleanPath, Posn)
+import Language.Preprocessor.Cpphs.Position (Posn)
 import Language.Preprocessor.Unlit as Unlit (unlit)
 
 
@@ -31,7 +31,7 @@
       preInc = case preInclude options of
                  [] -> ""
                  is -> concatMap (\f->"#include \""++f++"\"\n") is 
-                       ++ "#line 1 \""++cleanPath filename++"\"\n"
+                       ++ "#line 1 \""++filename++"\"\n"
 
   pass1 <- cppIfdef filename (defines options) (includes options) bools
                     (preInc++input)
@@ -58,7 +58,7 @@
       preInc = case preInclude options of
                  [] -> ""
                  is -> concatMap (\f->"#include \""++f++"\"\n") is 
-                       ++ "#line 1 \""++cleanPath filename++"\"\n"
+                       ++ "#line 1 \""++filename++"\"\n"
   (pass2,syms) <-
       if macros bools then do
           pass1 <- cppIfdef filename (defines options) (includes options)
diff --git a/cpphs.cabal b/cpphs.cabal
--- a/cpphs.cabal
+++ b/cpphs.cabal
@@ -1,5 +1,5 @@
 Name: cpphs
-Version: 1.20.3
+Version: 1.20.4
 Copyright: 2004-2017, Malcolm Wallace
 License: LGPL
 License-File: LICENCE-LGPL
@@ -24,7 +24,7 @@
 Extra-Source-Files: README, LICENCE-GPL, LICENCE-commercial, CHANGELOG, docs/cpphs.1, docs/index.html
 
 Library
-    Build-Depends: base>3&&<6, old-locale, old-time, directory, polyparse>=1.9
+    Build-Depends: base>3&&<6, old-locale, old-time, directory, filepath, polyparse>=1.9
     Exposed-Modules:
         Language.Preprocessor.Cpphs
         Language.Preprocessor.Unlit
@@ -40,7 +40,7 @@
         Language.Preprocessor.Cpphs.Tokenise
 
 Executable cpphs
-    Build-Depends: base>3&&<6, old-locale, old-time, directory, polyparse>=1.9
+    Build-Depends: base>3&&<6, old-locale, old-time, directory, filepath, polyparse>=1.9
     Main-Is: cpphs.hs
     Other-Modules:
         Language.Preprocessor.Cpphs
diff --git a/cpphs.hs b/cpphs.hs
--- a/cpphs.hs
+++ b/cpphs.hs
@@ -21,7 +21,7 @@
 import Data.List   ( isPrefixOf )
 
 version :: String
-version = "1.20.3"
+version = "1.20.4"
 
 main :: IO ()
 main = do