diff --git a/src/Data/Patch/IntMap.hs b/src/Data/Patch/IntMap.hs
index d46a006..b040534 100644
--- a/src/Data/Patch/IntMap.hs
+++ b/src/Data/Patch/IntMap.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE DeriveTraversable #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE TypeFamilies #-}
 -- | Module containing 'PatchIntMap', a 'Patch' for 'IntMap' which allows for
 -- insert/update or delete of associations.