diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+1.3.1
+=====
+  * Fix GHC 8.4 build.
+
 1.3.0
 =====
   * Move `EventNumber` to `Int64`.
diff --git a/eventsource-api.cabal b/eventsource-api.cabal
--- a/eventsource-api.cabal
+++ b/eventsource-api.cabal
@@ -1,11 +1,11 @@
--- This file has been generated from package.yaml by hpack version 0.20.0.
+-- This file has been generated from package.yaml by hpack version 0.28.2.
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 8d56f5720c87368ed15f3d659aefe82fc05bbb435f8157098aabfc2da595085b
+-- hash: 25d3e7c905840b2773e327d1dc91e90a9be3ecf9ff4c72ad67d8f999f0f05b9b
 
 name:           eventsource-api
-version:        1.3.0
+version:        1.3.1
 synopsis:       Provides an eventsourcing high level API.
 description:    A high-level eventsourcing library.
 category:       Eventsourcing
@@ -17,7 +17,6 @@
 license-file:   LICENSE.md
 build-type:     Simple
 cabal-version:  >= 1.10
-
 extra-source-files:
     CHANGELOG.md
     LICENSE.md
diff --git a/library/EventSource/Types.hs b/library/EventSource/Types.hs
--- a/library/EventSource/Types.hs
+++ b/library/EventSource/Types.hs
@@ -20,6 +20,7 @@
 import Data.Bifunctor (first)
 import Data.Foldable (foldlM)
 import Data.Int (Int64)
+import Data.Semigroup (Semigroup)
 import Data.String (IsString(..))
 import Data.String.Conversions (convertString)
 
@@ -111,11 +112,7 @@
 -- | Used to store a set a properties. One example is to be used as 'Event'
 --   metadata.
 newtype Properties = Properties (Map.Map Text Text)
-
---------------------------------------------------------------------------------
-instance Monoid Properties where
-  mempty = Properties mempty
-  mappend (Properties a) (Properties b) = Properties $ mappend a b
+  deriving (Semigroup, Monoid)
 
 --------------------------------------------------------------------------------
 instance Show Properties where
diff --git a/package.yaml b/package.yaml
--- a/package.yaml
+++ b/package.yaml
@@ -36,4 +36,4 @@
 maintainer: yo.eight@gmail.com
 name: eventsource-api
 synopsis: Provides an eventsourcing high level API.
-version: '1.3.0'
+version: '1.3.1'