diff --git a/StackSet.hs b/StackSet.hs
index f34c215..7b47e06 100644
--- a/StackSet.hs
+++ b/StackSet.hs
@@ -1,3 +1,5 @@
+{-# OPTIONS -fglasgow-exts #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  StackSet