diff --git a/open-typerep.cabal b/open-typerep.cabal
--- a/open-typerep.cabal
+++ b/open-typerep.cabal
@@ -1,5 +1,5 @@
 name:                open-typerep
-version:             0.3.2
+version:             0.3.3
 synopsis:            Open type representations and dynamic types
 description:         This package uses Data Types à la Carte to provide open type representations
                      and dynamic types/coercions for open type universes.
@@ -61,7 +61,8 @@
   build-depends:
     base        >=4 && <5,
     constraints >=0.3,
-    mtl         >=2.1,
+    mtl         >=2.2.1,
+      -- Smallest version that has Control.Monad.Except
     syntactic   >=3,
     tagged      >=0.4