diff --git a/lib/types/message-types.js b/lib/types/message-types.js
--- a/lib/types/message-types.js
+++ b/lib/types/message-types.js
@@ -335,6 +335,16 @@
   +sourceMessage: ComposableMessageInfo | RobotextMessageInfo,
 };
 
+export type ReactionMessageInfo = {
+  +type: 19,
+  +id: string,
+  +threadID: string,
+  +creator: RelativeUserInfo,
+  +time: number,
+  +targetMessageID: string,
+  +reaction: string | null,
+};
+
 export type MessageInfo =
   | ComposableMessageInfo
   | RobotextMessageInfo