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
@@ -564,39 +564,35 @@
   +newerThan?: ?number,
 };
 
+export type SimpleMessagesPayload = {
+  +rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
+  +truncationStatuses: MessageTruncationStatuses,
+};
+
 export type FetchMessageInfosRequest = {
   +cursors: ThreadCursors,
   +numberPerThread?: ?number,
 };
-export type FetchMessageInfosResponse = {
-  +rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
-  +truncationStatuses: MessageTruncationStatuses,
+export type FetchMessageInfosResponse = $ReadOnly<{
+  ...SimpleMessagesPayload,
   +userInfos: UserInfos,
-};
-export type FetchMessageInfosResult = {
-  +rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
-  +truncationStatuses: MessageTruncationStatuses,
-};
+}>;
+export type FetchMessageInfosResult = SimpleMessagesPayload;
 export type FetchMessageInfosPayload = {
   +threadID: string,
   +rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
   +truncationStatus: MessageTruncationStatus,
 };
-export type MessagesResponse = {
-  +rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
-  +truncationStatuses: MessageTruncationStatuses,
+export type MessagesResponse = $ReadOnly<{
+  ...SimpleMessagesPayload,
   +currentAsOf: number,
-};
+}>;
 export const messagesResponseValidator: TInterface<MessagesResponse> =
   tShape<MessagesResponse>({
     rawMessageInfos: t.list(rawMessageInfoValidator),
     truncationStatuses: messageTruncationStatusesValidator,
     currentAsOf: t.Number,
   });
-export type SimpleMessagesPayload = {
-  +rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
-  +truncationStatuses: MessageTruncationStatuses,
-};
 export const defaultNumberPerThread = 20;
 export const defaultMaxMessageAge = 14 * 24 * 60 * 60 * 1000; // 2 weeks