diff --git a/src/Network/Wai/Handler/WarpTLS/UserId.hs b/src/Network/Wai/Handler/WarpTLS/UserId.hs
--- a/src/Network/Wai/Handler/WarpTLS/UserId.hs
+++ b/src/Network/Wai/Handler/WarpTLS/UserId.hs
@@ -6,6 +6,7 @@
 
 import Control.Arrow ((***), (&&&))
 import Control.Exception (bracket)
+import Data.Semigroup ((<>))
 import Data.List (unfoldr)
 import Data.Streaming.Network (bindPortTCP)
 import System.Posix (
diff --git a/warp-tls-uid.cabal b/warp-tls-uid.cabal
--- a/warp-tls-uid.cabal
+++ b/warp-tls-uid.cabal
@@ -2,10 +2,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: df4da9c6b167a85ea51e282d41e7250768ca1fbde66c674a874eef4a4c5cab5a
+-- hash: b4a9df2452b824bd2849823488685af56b31c74ddd4656e48ff3ca3247ba4094
 
 name:           warp-tls-uid
-version:        0.2.0.3
+version:        0.2.0.4
 synopsis:       set group and user id before running server
 description:    Please see the README on GitHub at <https://github.com/YoshikuniJujo/warp-tls-uid#readme>
 category:       Web