diff --git a/concurrent-state.cabal b/concurrent-state.cabal
--- a/concurrent-state.cabal
+++ b/concurrent-state.cabal
@@ -1,5 +1,5 @@
 name:                concurrent-state
-version:             0.3.1.0
+version:             0.3.1.1
 synopsis:            MTL-like library using TVars
 description:         State and Writer backed by TVars.
 homepage:            https://github.com/joelteon/concurrent-state
@@ -15,7 +15,7 @@
   exposed-modules:     Control.Monad.State.Concurrent
                        Control.Monad.State.Concurrent.Lazy
                        Control.Monad.State.Concurrent.Strict
-  build-depends:       base >=4.6 && <4.7, mtl, stm, transformers
+  build-depends:       base >=4.6 && <4.7, mtl >= 2.1, stm, transformers
   hs-source-dirs:      src
   default-language:    Haskell2010