diff --git a/HpcParser.y b/HpcParser.y
index b4d8c79518fa1e7396e6f2933b66438fa6c75dcc..01307bf565d17a1f14c934c9c8d962ebf5923b34 100644
--- a/HpcParser.y
+++ b/HpcParser.y
@@ -1,4 +1,5 @@
 { 
+{-# LANGUAGE BangPatterns #-} -- required for versions of Happy before 1.18.6
 {-# OPTIONS -Wwarn -XNoMonomorphismRestriction #-}
 -- The NoMonomorphismRestriction deals with a Happy infelicity
 --    With OutsideIn's more conservativ monomorphism restriction