1 files changed, 2 insertions, 0 deletions
diff --git a/StackSet.hs b/StackSet.hs
index 5caea7e..1dd4579 100644
--- a/StackSet.hs
+++ b/StackSet.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE PatternGuards #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  StackSet