diff --git a/System/FilePath/Internal.hs b/System/FilePath/Internal.hs
--- a/System/FilePath/Internal.hs
+++ b/System/FilePath/Internal.hs
@@ -601,6 +601,7 @@
 -- > splitFileName "bob" == ("./", "bob")
 -- > Posix:   splitFileName "/" == ("/","")
 -- > Windows: splitFileName "c:" == ("c:","")
+-- > Windows: splitFileName "\\\\?\\A:\\fred" == ("\\\\?\\A:\\","fred")
 splitFileName :: FILEPATH -> (STRING, STRING)
 splitFileName x = if null path
     then (dotSlash, file)
@@ -648,12 +649,15 @@
   -- If bs' is empty, then s2 as the last character of dirSlash must be a path separator,
   -- so we are in the middle of shared drive.
   -- Otherwise, since s1 is a path separator, we might be in the middle of UNC path.
-  , null bs' || maybe False (null . snd) (readDriveUNC dirSlash)
+  , null bs' || maybe False isIncompleteUNC (readDriveUNC dirSlash)
   = (fp, mempty)
   | otherwise
   = (dirSlash, file)
   where
     (dirSlash, file) = breakEnd isPathSeparator fp
+
+    isIncompleteUNC (pref, suff) = null suff && not (hasPenultimateColon pref)
+    hasPenultimateColon = maybe False (maybe False ((== _colon) . snd) . unsnoc . fst) . unsnoc
 
 -- | Set the filename.
 --
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -2,6 +2,10 @@
 
 _Note: below all `FilePath` values are unquoted, so `\\` really means two backslashes._
 
+## 1.4.100.3 *Feb 2023*
+
+* Fix a regression in `splitFileName` wrt [#189](https://github.com/haskell/filepath/pull/189)
+
 ## 1.4.100.2 *Feb 2023*
 
 * Speed up `splitFileName`, `splitExtension`, `readDriveLetter` and various other helpers (up to 20x faster) by @Bodigrim
diff --git a/filepath.cabal b/filepath.cabal
--- a/filepath.cabal
+++ b/filepath.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.2
 name:               filepath
-version:            1.4.100.2
+version:            1.4.100.3
 
 -- NOTE: Don't forget to update ./changelog.md
 license:            BSD-3-Clause
diff --git a/tests/filepath-tests/TestGen.hs b/tests/filepath-tests/TestGen.hs
--- a/tests/filepath-tests/TestGen.hs
+++ b/tests/filepath-tests/TestGen.hs
@@ -456,6 +456,8 @@
     ,("AFP_P.splitFileName (\"/\") == ((\"/\"), (\"\"))", property $ AFP_P.splitFileName ("/") == (("/"), ("")))
     ,("W.splitFileName \"c:\" == (\"c:\", \"\")", property $ W.splitFileName "c:" == ("c:", ""))
     ,("AFP_W.splitFileName (\"c:\") == ((\"c:\"), (\"\"))", property $ AFP_W.splitFileName ("c:") == (("c:"), ("")))
+    ,("W.splitFileName \"\\\\\\\\?\\\\A:\\\\fred\" == (\"\\\\\\\\?\\\\A:\\\\\", \"fred\")", property $ W.splitFileName "\\\\?\\A:\\fred" == ("\\\\?\\A:\\", "fred"))
+    ,("AFP_W.splitFileName (\"\\\\\\\\?\\\\A:\\\\fred\") == ((\"\\\\\\\\?\\\\A:\\\\\"), (\"fred\"))", property $ AFP_W.splitFileName ("\\\\?\\A:\\fred") == (("\\\\?\\A:\\"), ("fred")))
     ,("P.replaceFileName \"/directory/other.txt\" \"file.ext\" == \"/directory/file.ext\"", property $ P.replaceFileName "/directory/other.txt" "file.ext" == "/directory/file.ext")
     ,("W.replaceFileName \"/directory/other.txt\" \"file.ext\" == \"/directory/file.ext\"", property $ W.replaceFileName "/directory/other.txt" "file.ext" == "/directory/file.ext")
     ,("AFP_P.replaceFileName (\"/directory/other.txt\") (\"file.ext\") == (\"/directory/file.ext\")", property $ AFP_P.replaceFileName ("/directory/other.txt") ("file.ext") == ("/directory/file.ext"))