diff --git a/extractable-singleton.cabal b/extractable-singleton.cabal
--- a/extractable-singleton.cabal
+++ b/extractable-singleton.cabal
@@ -1,5 +1,5 @@
 name:                extractable-singleton
-version:             0.0.0.1
+version:             0.0.1
 synopsis:            A functor, where the "stored" value is isomorphic to Identity
 -- description:
 homepage:            https://github.com/athanclark/extractable-singleton#readme
@@ -17,6 +17,7 @@
   hs-source-dirs:      src
   exposed-modules:     Data.Singleton.Class
   build-depends:       base >= 4.8 && < 5
+                     , transformers
   default-language:    Haskell2010
 
 source-repository head