diff --git a/src/MessagePack.UnityClient/Assets/Scripts/MessagePack/MessagePackSerializer.cs b/src/MessagePack.UnityClient/Assets/Scripts/MessagePack/MessagePackSerializer.cs
index ae5a50369..a75917b0b 100644
--- a/src/MessagePack.UnityClient/Assets/Scripts/MessagePack/MessagePackSerializer.cs
+++ b/src/MessagePack.UnityClient/Assets/Scripts/MessagePack/MessagePackSerializer.cs
@@ -440,7 +440,7 @@ private static T DeserializeFromSequenceAndRewindStreamIfPossible<T>(Stream stre
             if (streamToRewind.CanSeek && !reader.End)
             {
                 // Reverse the stream as many bytes as we left unread.
-                int bytesNotRead = checked((int)reader.Sequence.Slice(reader.Position).Length);
+                long bytesNotRead = reader.Sequence.Slice(reader.Position).Length;
                 streamToRewind.Seek(-bytesNotRead, SeekOrigin.Current);
             }