diff --git a/Data/Graph/Inductive/PatriciaTree.hs b/Data/Graph/Inductive/PatriciaTree.hs
index 2e68d86..c465259 100644
--- a/Data/Graph/Inductive/PatriciaTree.hs
+++ b/Data/Graph/Inductive/PatriciaTree.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE BangPatterns #-}
 
 -- |An efficient implementation of 'Data.Graph.Inductive.Graph.Graph'
 -- using big-endian patricia tree (i.e. "Data.IntMap").