diff --git a/pre-commit b/pre-commit
new file mode 100755
index 0000000..c7ff367
--- /dev/null
+++ b/pre-commit
@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+
+
+tmp=$(mktemp)
+
+
+find src/ -type f | while read f; do
+    if ! ormolu --mode check "$f"; then
+        echo "$f is not properly formatted"
+        echo 1 > "$tmp"
+    fi
+done
+
+
+if test "X1" = "X$(cat "$tmp")"; then
+    exit 1
+fi
diff --git a/src/Main.hs b/src/Main.hs
index 5e045a4..fd53534 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -2,11 +2,11 @@
 {-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE OverloadedStrings #-}
 
-import Protolude hiding (for)
-import Pretty
-import WS19
 import Pipes
+import Pretty
+import Protolude hiding (for)
 import System.IO
+import WS19
 
 mkPop = population 100 (I prios [])
 
@@ -16,7 +16,7 @@ main = do
   let t = fromMaybe 100 $ headMay args >>= readMaybe
   hSetBuffering stdout NoBuffering
   pop <- mkPop
-  pop' <- runEffect $ for (run 2 1 (5/100) pop (steps t)) log
+  pop' <- runEffect $ for (run 2 1 (5 / 100) pop (steps t)) log
   (res, _) <- bests 5 pop'
   sequence_ $ format <$> res
   where
diff --git a/src/Pretty.hs b/src/Pretty.hs
index 109109b..a46cdcd 100644
--- a/src/Pretty.hs
+++ b/src/Pretty.hs
@@ -1,11 +1,8 @@
 {-# LANGUAGE NoImplicitPrelude #-}
 
-
 module Pretty where
 
-
 import Protolude
 
-
 class Pretty a where
   pretty :: a -> Text
diff --git a/src/Seminar.hs b/src/Seminar.hs
index c72bc1c..1f0fa84 100644
--- a/src/Seminar.hs
+++ b/src/Seminar.hs
@@ -28,7 +28,7 @@ instance Pretty (Maybe Topic) where
   pretty (Just t) = t
   pretty Nothing = "Kein Thema"
 
-newtype Priorities = P { unP ::  [(Student, [(Topic, Int)])] }
+newtype Priorities = P {unP :: [(Student, [(Topic, Int)])]}
   deriving (Eq, Show)
 
 instance Arbitrary Priorities where
diff --git a/src/Test.hs b/src/Test.hs
index c320594..e0a921d 100644
--- a/src/Test.hs
+++ b/src/Test.hs
@@ -2,9 +2,9 @@
 
 module Main where
 
+import qualified GA
 import Protolude
 import qualified Seminar
-import qualified GA
 
 main :: IO ()
 main = do