diff --git a/src/Physics/ForceLayout.hs b/src/Physics/ForceLayout.hs
index a3bc692..5acce08 100644
--- a/src/Physics/ForceLayout.hs
+++ b/src/Physics/ForceLayout.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE FlexibleContexts     #-}
 {-# LANGUAGE ScopedTypeVariables  #-}
 {-# LANGUAGE TemplateHaskell      #-}
+{-# LANGUAGE TypeFamilies         #-}
 {-# LANGUAGE UndecidableInstances #-}
 
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