diff --git a/charset.cabal b/charset.cabal
--- a/charset.cabal
+++ b/charset.cabal
@@ -1,5 +1,5 @@
 name:          charset
-version:       0.3.4
+version:       0.3.5
 license:       BSD3
 license-File:  LICENSE
 copyright:     (c) Edward Kmett 2010-2012
diff --git a/src/Data/CharSet.hs b/src/Data/CharSet.hs
--- a/src/Data/CharSet.hs
+++ b/src/Data/CharSet.hs
@@ -1,4 +1,8 @@
 {-# OPTIONS_GHC -fspec-constr #-}
+{-# LANGUAGE CPP #-}
+#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 702
+{-# LANGUAGE Trustworthy #-}
+#endif
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.CharSet
diff --git a/src/Data/CharSet/ByteSet.hs b/src/Data/CharSet/ByteSet.hs
--- a/src/Data/CharSet/ByteSet.hs
+++ b/src/Data/CharSet/ByteSet.hs
@@ -1,4 +1,8 @@
 {-# LANGUAGE BangPatterns, MagicHash #-}
+{-# LANGUAGE CPP #-}
+#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 702
+{-# LANGUAGE Trustworthy #-}
+#endif
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.CharSet.ByteSet