diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Revision history for blucontrol
 
+## 0.2.1.0 -- 2020-08-12
+
+* Compile user config only when it has been modified.
+* New internal module `Blucontrol.Main.GHC.Internal` for setting ghc flags.
+
 ## 0.2.0.0 -- 2020-08-10
 
 * Rename the whole application from bludigon to blucontrol.
diff --git a/blucontrol.cabal b/blucontrol.cabal
--- a/blucontrol.cabal
+++ b/blucontrol.cabal
@@ -1,5 +1,5 @@
 name:                blucontrol
-version:             0.2.0.0
+version:             0.2.1.0
 synopsis:            Configurable blue light filter
 description:         This application is a blue light filter, with the main focus on
                      configurability.
@@ -41,7 +41,8 @@
                        Blucontrol.Recolor.X
                        Blucontrol.RGB
                        Blucontrol.RGB.Temperature
-  other-modules:       Blucontrol.Recolor.X.Internal
+  other-modules:       Blucontrol.Main.GHC.Internal
+                       Blucontrol.Recolor.X.Internal
                        Paths_blucontrol
   build-depends:       base              >= 4.11    && < 5
                      , containers        >= 0.6.2.1 && < 0.7
diff --git a/src/Blucontrol/Main/CLI.hs b/src/Blucontrol/Main/CLI.hs
--- a/src/Blucontrol/Main/CLI.hs
+++ b/src/Blucontrol/Main/CLI.hs
@@ -3,10 +3,11 @@
 ) where
 
 import Control.DeepSeq
+import Control.Monad (when)
 import Data.Version (showVersion)
 import GHC.Generics
 import System.Console.GetOpt
-import System.Directory (XdgDirectory (..), createDirectoryIfMissing, doesFileExist, getXdgDirectory)
+import System.Directory (XdgDirectory (..), createDirectoryIfMissing, doesFileExist, getModificationTime, getXdgDirectory)
 import System.Environment (getArgs, getProgName)
 import System.Exit (ExitCode (..), exitFailure, exitSuccess)
 import System.FilePath ((</>))
@@ -14,6 +15,7 @@
 import System.Posix.Process (executeFile)
 import System.Process (runProcess, waitForProcess)
 
+import Blucontrol.Main.GHC.Internal
 import Paths_blucontrol (version)
 
 data Flag = Help
@@ -61,27 +63,31 @@
 build = do
   configPath <- (</> configLeafname) <$> getXdgDir XdgConfig
   configExists <- doesFileExist configPath
-  if configExists
-     then do progName <- getProgName
-             if progName == compiledConfigLeafname
-                then return ()
-                else do compile
-                        cacheDir <- getXdgDir XdgCache
-                        executeFile (cacheDir </> compiledConfigLeafname) False [] Nothing
-     else return ()
+  when configExists $ do
+    progName <- getProgName
+    compiledConfigPath <- (</> compiledConfigLeafname) <$> getXdgDir XdgCache
+    if progName == compiledConfigLeafname
+       then do configTime <- getModificationTime configPath -- TODO: getModificationTime can fail
+               compiledConfigTime <- getModificationTime compiledConfigPath
+               when (configTime > compiledConfigTime) $ do
+                 compile
+                 executeFile compiledConfigPath False [] Nothing
+       else do compile
+               executeFile compiledConfigPath False [] Nothing
 
 compile :: IO ()
 compile = do
   configDir <- getXdgDir XdgConfig
   cacheDir <- getXdgDir XdgCache
   createDirectoryIfMissing False cacheDir
+  let ghcFlags = [ "--make"
+                 , configLeafname
+                 , "-main-is", "main"
+                 , "-v0"
+                 , "-o", cacheDir </> compiledConfigLeafname
+                 ] <> ghcAdditionalFlags
   status <- waitForProcess =<<
-    runProcess "ghc" [ "--make"
-                     , configLeafname
-                     , "-main-is", "main"
-                     , "-v0"
-                     , "-o", cacheDir </> compiledConfigLeafname
-                     ] (Just configDir) Nothing Nothing Nothing Nothing
+    runProcess ghcBinary ghcFlags (Just configDir) Nothing Nothing Nothing Nothing
   case status of
     ExitSuccess -> return ()
     ExitFailure _ -> exitFailure
diff --git a/src/Blucontrol/Main/GHC/Internal.hs b/src/Blucontrol/Main/GHC/Internal.hs
new file mode 100644
--- /dev/null
+++ b/src/Blucontrol/Main/GHC/Internal.hs
@@ -0,0 +1,11 @@
+module Blucontrol.Main.GHC.Internal (
+  ghcBinary
+, ghcAdditionalFlags
+) where
+
+ghcBinary :: String
+ghcBinary = "ghc"
+
+ghcAdditionalFlags :: [String]
+ghcAdditionalFlags = [
+                     ]