diff --git a/machines.cabal b/machines.cabal
--- a/machines.cabal
+++ b/machines.cabal
@@ -1,6 +1,6 @@
 name:          machines
 category:      Control, Enumerator
-version:       0.1.1
+version:       0.1.2
 license:       BSD3
 cabal-version: >= 1.10
 license-file:  LICENSE
@@ -32,7 +32,7 @@
     base         == 4.*,
     comonad      == 3.0.*,
     containers   >= 0.3   && < 0.6,
-    free         >= 3.1.1 && < 3.2,
+    free         >= 3.1.1 && < 3.3,
     profunctors  == 3.0.*,
     semigroups   >= 0.8.3 && < 0.9,
     transformers == 0.3.*,
diff --git a/src/Data/Machine/Unread.hs b/src/Data/Machine/Unread.hs
--- a/src/Data/Machine/Unread.hs
+++ b/src/Data/Machine/Unread.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE GADTs #-}
+{-# LANGUAGE Rank2Types #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.Machine.Unread