diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,7 @@
+0.6.1:
+	* Add 'addFileExtension' function and its operator form: (<.>).
+	* Derive 'Eq' instance for 'PathException'.
+
 0.6.0:
 
 	* Deprecate PathParseException and rename it to PathException
@@ -45,7 +49,7 @@
 
 0.2.0:
 
-        * Rename parentAbs to simply parent.
+	* Rename parentAbs to simply parent.
 	* Add dirname.
 
 0.3.0:
diff --git a/path.cabal b/path.cabal
--- a/path.cabal
+++ b/path.cabal
@@ -1,5 +1,5 @@
 name:                path
-version:             0.6.0
+version:             0.6.1
 synopsis:            Support for well-typed paths
 description:         Support for well-typed paths.
 license:             BSD3
diff --git a/src/Path.hs b/src/Path.hs
--- a/src/Path.hs
+++ b/src/Path.hs
@@ -49,6 +49,8 @@
   ,filename
   ,dirname
   ,fileExtension
+  ,addFileExtension
+  ,(<.>)
   ,setFileExtension
   ,(-<.>)
    -- * Parsing
@@ -138,7 +140,7 @@
   | InvalidAbsFile FilePath
   | InvalidRelFile FilePath
   | NotAProperPrefix FilePath FilePath
-  deriving (Show,Typeable)
+  deriving (Show,Eq,Typeable)
 instance Exception PathException
 
 --------------------------------------------------------------------------------
@@ -330,6 +332,50 @@
 fileExtension :: Path b File -> String
 fileExtension = FilePath.takeExtension . toFilePath
 
+-- | Add extension to given file path. Throws if the
+-- resulting filename does not parse.
+--
+-- >>> addFileExtension "txt $(mkRelFile "foo")
+-- "foo.txt"
+-- >>> addFileExtension "symbols" $(mkRelFile "Data.List")
+-- "Data.List.symbols"
+-- >>> addFileExtension ".symbols" $(mkRelFile "Data.List")
+-- "Data.List.symbols"
+-- >>> addFileExtension "symbols" $(mkRelFile "Data.List.")
+-- "Data.List..symbols"
+-- >>> addFileExtension ".symbols" $(mkRelFile "Data.List.")
+-- "Data.List..symbols"
+-- >>> addFileExtension "evil/" $(mkRelFile "Data.List")
+-- *** Exception: InvalidRelFile "Data.List.evil/"
+--
+-- @since 0.6.1
+addFileExtension :: MonadThrow m
+  => String            -- ^ Extension to add
+  -> Path b File       -- ^ Old file name
+  -> m (Path b File)   -- ^ New file name with the desired extension added at the end
+addFileExtension ext (Path path) =
+  if FilePath.isAbsolute path
+    then liftM coercePath (parseAbsFile (FilePath.addExtension path ext))
+    else liftM coercePath (parseRelFile (FilePath.addExtension path ext))
+  where coercePath :: Path a b -> Path a' b'
+        coercePath (Path a) = Path a
+
+-- | A synonym for 'addFileExtension' in the form of an operator.
+-- See more examples there.
+--
+-- >>> $(mkRelFile "Data.List") <.> "symbols"
+-- "Data.List.symbols"
+-- >>> $(mkRelFile "Data.List") <.> "evil/"
+-- *** Exception: InvalidRelFile "Data.List.evil/"
+--
+-- @since 0.6.1
+infixr 7 <.>
+(<.>) :: MonadThrow m
+  => Path b File       -- ^ Old file name
+  -> String            -- ^ Extension to add
+  -> m (Path b File)   -- ^ New file name with the desired extension added at the end
+(<.>) = flip addFileExtension
+
 -- | Replace\/add extension to given file path. Throws if the
 -- resulting filename does not parse.
 --
@@ -518,7 +564,6 @@
     Left err -> error (show err)
     Right (Path str) ->
       [|Path $(return (LitE (StringL str))) :: Path Rel File|]
-
 
 --------------------------------------------------------------------------------
 -- Internal functions
diff --git a/test/Posix.hs b/test/Posix.hs
--- a/test/Posix.hs
+++ b/test/Posix.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE QuasiQuotes #-}
@@ -29,6 +30,7 @@
      describe "Operations: parent" operationParent
      describe "Operations: filename" operationFilename
      describe "Operations: dirname" operationDirname
+     describe "Operations: addFileExtension" operationAddFileExtension
      describe "Operations: setFileExtension" operationSetFileExtension
      describe "Restrictions" restrictions
      describe "Aeson Instances" aesonInstances
@@ -177,6 +179,36 @@
         (toFilePath $(mkRelDir ".") == "./")
      it "show $(mkRelDir \".\") == \"\\\"./\\\"\""
         (show $(mkRelDir ".") == "\"./\"")
+
+operationAddFileExtension :: Spec
+operationAddFileExtension = do
+  it "adds extension if there is none" $
+    addFileExtension "ext" $(mkAbsFile "/directory/path")
+      `shouldReturn` $(mkAbsFile "/directory/path.ext")
+  it "adds extension if there is already one" $
+    addFileExtension "baz" $(mkRelFile "foo.bar")
+      `shouldReturn` $(mkRelFile "foo.bar.baz")
+  it "adds extension with dot" $
+    addFileExtension ".bar" $(mkRelFile "foo")
+      `shouldReturn` $(mkRelFile "foo.bar")
+  it "adds extension with dot after dot" $
+    $(mkRelFile "foo.") <.> ".bar"
+      `shouldReturn` $(mkRelFile "foo..bar")
+  it "adds extension without dot after dot" $
+    $(mkRelFile "foo.") <.> "bar"
+      `shouldReturn` $(mkRelFile "foo..bar")
+  it "adds extension with separator" $  -- I'm not sure it's okay
+    $(mkRelFile "foo") <.> "evil/extension"
+      `shouldReturn` $(mkRelFile "foo.evil/extension")
+  it "adds extension to file inside dotted directory" $
+    $(mkRelFile "foo.bar/baz") <.> "txt"
+      `shouldReturn` $(mkRelFile "foo.bar/baz.txt")
+  it "throws InvalidRelFile extension if extenstion ends with /" $
+    $(mkRelFile "foo") <.> "evil/"
+      `shouldThrow` (== InvalidRelFile "foo.evil/")
+  it "throws InvalidAbsFile extension if extenstion ends with /" $
+    $(mkAbsFile "/home/cfg") <.> "txt/" -- No Eq instance for PathException
+      `shouldThrow` (== InvalidAbsFile "/home/cfg.txt/")
 
 operationSetFileExtension :: Spec
 operationSetFileExtension = do
diff --git a/test/Windows.hs b/test/Windows.hs
--- a/test/Windows.hs
+++ b/test/Windows.hs
@@ -1,6 +1,7 @@
-{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE LambdaCase          #-}
+{-# LANGUAGE QuasiQuotes         #-}
 {-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE QuasiQuotes #-}
+{-# LANGUAGE TemplateHaskell     #-}
 
 -- | Test suite.
 
@@ -29,6 +30,7 @@
      describe "Operations: parent" operationParent
      describe "Operations: filename" operationFilename
      describe "Operations: dirname" operationDirname
+     describe "Operations: addFileExtension" operationAddFileExtension
      describe "Operations: setFileExtension" operationSetFileExtension
      describe "Restrictions" restrictions
      describe "Aeson Instances" aesonInstances
@@ -122,7 +124,6 @@
      it "not (\\ `isProperPrefixOf` \\)"
         (not (isProperPrefixOf $(mkAbsDir "C:\\") $(mkAbsDir "C:\\")))
 
-
 -- | The 'stripProperPrefix' operation.
 operationStripProperPrefix :: Spec
 operationStripProperPrefix =
@@ -175,6 +176,36 @@
         (toFilePath $(mkRelDir ".") == ".\\")
      it "show $(mkRelDir \".\") == \"\\\".\\\\\"\""
         (show $(mkRelDir ".") == "\".\\\\\"")
+
+operationAddFileExtension :: Spec
+operationAddFileExtension = do
+  it "adds extension if there is none" $
+    addFileExtension "ext" $(mkAbsFile "C:\\directory\\path")
+      `shouldReturn` $(mkAbsFile "C:\\directory\\path.ext")
+  it "adds extension if there is already one" $
+    addFileExtension "baz" $(mkRelFile "foo.bar")
+      `shouldReturn` $(mkRelFile "foo.bar.baz")
+  it "adds extension with dot" $
+    addFileExtension ".bar" $(mkRelFile "foo")
+      `shouldReturn` $(mkRelFile "foo.bar")
+  it "adds extension with dot after dot" $
+    $(mkRelFile "foo.") <.> ".bar"
+      `shouldReturn` $(mkRelFile "foo..bar")
+  it "adds extension without dot after dot" $
+    $(mkRelFile "foo.") <.> "bar"
+      `shouldReturn` $(mkRelFile "foo..bar")
+  it "adds extension with separator" $  -- I'm not sure it's okay
+    $(mkRelFile "foo") <.> "evil\\extension"
+      `shouldReturn` $(mkRelFile "foo.evil\\extension")
+  it "adds extension to file inside dotted directory" $
+    $(mkRelFile "foo.bar\\baz") <.> "txt"
+      `shouldReturn` $(mkRelFile "foo.bar\\baz.txt")
+  it "throws InvalidRelFile extension if extenstion ends with \\" $
+    $(mkRelFile "foo") <.> "evil\\"
+      `shouldThrow` (== InvalidRelFile "foo.evil\\")
+  it "throws InvalidAbsFile extension if extenstion ends with \\" $
+    $(mkAbsFile "C:\\home\\cfg") <.> "txt\\"
+      `shouldThrow` (== InvalidAbsFile "C:\\home\\cfg.txt\\")
 
 operationSetFileExtension :: Spec
 operationSetFileExtension = do