diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+1.3.0
+=====
+  * Move `EventNumber` to `Int64`.
+
 1.2.0
 =====
   * Introduce Aggregate API.
diff --git a/eventsource-api.cabal b/eventsource-api.cabal
--- a/eventsource-api.cabal
+++ b/eventsource-api.cabal
@@ -2,10 +2,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 210f402f20d9901165999ae9e117c9e55c55fc725f1ecf4f895f42ec9c3e41d0
+-- hash: 8d56f5720c87368ed15f3d659aefe82fc05bbb435f8157098aabfc2da595085b
 
 name:           eventsource-api
-version:        1.2.0
+version:        1.3.0
 synopsis:       Provides an eventsourcing high level API.
 description:    A high-level eventsourcing library.
 category:       Eventsourcing
diff --git a/library/EventSource/Types.hs b/library/EventSource/Types.hs
--- a/library/EventSource/Types.hs
+++ b/library/EventSource/Types.hs
@@ -19,7 +19,7 @@
 import Control.Monad (MonadPlus, mzero)
 import Data.Bifunctor (first)
 import Data.Foldable (foldlM)
-import Data.Int (Int32)
+import Data.Int (Int64)
 import Data.String (IsString(..))
 import Data.String.Conversions (convertString)
 
@@ -235,7 +235,7 @@
 
 --------------------------------------------------------------------------------
 -- | Represents an event index in a stream.
-newtype EventNumber = EventNumber Int32
+newtype EventNumber = EventNumber Int64
   deriving (Eq, Ord, Num, Enum, Show, FromJSON, ToJSON)
 
 --------------------------------------------------------------------------------
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: '1.2.0'
+version: '1.3.0'