diff --git a/ghc-mod.cabal b/ghc-mod.cabal
--- a/ghc-mod.cabal
+++ b/ghc-mod.cabal
@@ -1,5 +1,5 @@
 Name:                   ghc-mod
-Version:                2.1.0
+Version:                2.1.1
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3
@@ -60,6 +60,7 @@
   Build-Depends:        base >= 4.0 && < 5
                       , Cabal >= 1.10
                       , containers
+                      , convertible
                       , directory
                       , filepath
                       , ghc