diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,10 @@
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## 0.6.4
+### Fixed
+- Import `Control.Monad` to fix `mtl-2.3` issue.
+
 ## 0.6.3
 ### Changed
 - Add `publish` and `publishSTM` functions.
diff --git a/nqe.cabal b/nqe.cabal
--- a/nqe.cabal
+++ b/nqe.cabal
@@ -1,13 +1,13 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.33.0.
+-- This file has been generated from package.yaml by hpack version 0.34.4.
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: b8bfeb3e2d85e7de9f577f583e4e83d00fb5c564b58716c2fdc26e0da0c6ced0
+-- hash: 3792a9b030f7697ae24ef34aef1c83768206ff91344fe288987266195c699f0a
 
 name:           nqe
-version:        0.6.3
+version:        0.6.4
 synopsis:       Concurrency library in the style of Erlang/OTP
 description:    Please see the README on GitHub at <https://github.com/jprupp/nqe#readme>
 category:       Control
diff --git a/src/Control/Concurrent/NQE/Publisher.hs b/src/Control/Concurrent/NQE/Publisher.hs
--- a/src/Control/Concurrent/NQE/Publisher.hs
+++ b/src/Control/Concurrent/NQE/Publisher.hs
@@ -32,6 +32,7 @@
 
 import           Control.Concurrent.NQE.Process
 import           Control.Concurrent.Unique
+import           Control.Monad
 import           Control.Monad.Reader
 import           Data.Function
 import           Data.Hashable