diff --git a/keyserver/src/responders/message-responders.js b/keyserver/src/responders/message-responders.js
--- a/keyserver/src/responders/message-responders.js
+++ b/keyserver/src/responders/message-responders.js
@@ -78,7 +78,7 @@
     throw new ServerError('invalid_parameters');
   }
 
-  const messageData: TextMessageData = {
+  let messageData: TextMessageData = {
     type: messageTypes.TEXT,
     threadID,
     creatorID: viewer.id,
@@ -86,7 +86,7 @@
     text,
   };
   if (localID) {
-    messageData.localID = localID;
+    messageData = { ...messageData, localID };
   }
   const rawMessageInfos = await createMessages(viewer, [messageData]);
 
diff --git a/lib/shared/message-utils.js b/lib/shared/message-utils.js
--- a/lib/shared/message-utils.js
+++ b/lib/shared/message-utils.js
@@ -263,6 +263,9 @@
       time,
       media: photoMedia,
     }: ImagesMessageData);
+    if (localID) {
+      messageData = { ...messageData, localID };
+    }
   } else {
     messageData = ({
       type: messageTypes.MULTIMEDIA,
@@ -271,9 +274,9 @@
       time,
       media: input.media,
     }: MediaMessageData);
-  }
-  if (localID) {
-    messageData.localID = localID;
+    if (localID) {
+      messageData = { ...messageData, localID };
+    }
   }
   return messageData;
 }
diff --git a/lib/shared/messages/multimedia-message-spec.js b/lib/shared/messages/multimedia-message-spec.js
--- a/lib/shared/messages/multimedia-message-spec.js
+++ b/lib/shared/messages/multimedia-message-spec.js
@@ -92,7 +92,7 @@
       `media_infos must be defined`,
     );
 
-    const rawMessageInfo: RawImagesMessageInfo | RawMediaMessageInfo =
+    let rawMessageInfo: RawImagesMessageInfo | RawMediaMessageInfo =
       messageType === messageTypes.IMAGES
         ? {
             type: messageTypes.IMAGES,
@@ -113,10 +113,16 @@
           };
 
     if (clientDBMessageInfo.local_id) {
-      rawMessageInfo.localID = clientDBMessageInfo.local_id;
+      rawMessageInfo = {
+        ...rawMessageInfo,
+        localID: clientDBMessageInfo.local_id,
+      };
     }
     if (clientDBMessageInfo.id !== clientDBMessageInfo.local_id) {
-      rawMessageInfo.id = clientDBMessageInfo.id;
+      rawMessageInfo = {
+        ...rawMessageInfo,
+        id: clientDBMessageInfo.id,
+      };
     }
     return rawMessageInfo;
   },
@@ -150,7 +156,7 @@
     creator: RelativeUserInfo,
   ): ?(MediaMessageInfo | ImagesMessageInfo) {
     if (rawMessageInfo.type === messageTypes.IMAGES) {
-      const messageInfo: ImagesMessageInfo = {
+      let messageInfo: ImagesMessageInfo = {
         type: messageTypes.IMAGES,
         threadID: rawMessageInfo.threadID,
         creator,
@@ -158,14 +164,14 @@
         media: rawMessageInfo.media,
       };
       if (rawMessageInfo.id) {
-        messageInfo.id = rawMessageInfo.id;
+        messageInfo = { ...messageInfo, id: rawMessageInfo.id };
       }
       if (rawMessageInfo.localID) {
-        messageInfo.localID = rawMessageInfo.localID;
+        messageInfo = { ...messageInfo, localID: rawMessageInfo.localID };
       }
       return messageInfo;
     } else if (rawMessageInfo.type === messageTypes.MULTIMEDIA) {
-      const messageInfo: MediaMessageInfo = {
+      let messageInfo: MediaMessageInfo = {
         type: messageTypes.MULTIMEDIA,
         threadID: rawMessageInfo.threadID,
         creator,
@@ -173,10 +179,10 @@
         media: rawMessageInfo.media,
       };
       if (rawMessageInfo.id) {
-        messageInfo.id = rawMessageInfo.id;
+        messageInfo = { ...messageInfo, id: rawMessageInfo.id };
       }
       if (rawMessageInfo.localID) {
-        messageInfo.localID = rawMessageInfo.localID;
+        messageInfo = { ...messageInfo, localID: rawMessageInfo.localID };
       }
       return messageInfo;
     }
diff --git a/lib/shared/messages/text-message-spec.js b/lib/shared/messages/text-message-spec.js
--- a/lib/shared/messages/text-message-spec.js
+++ b/lib/shared/messages/text-message-spec.js
@@ -100,7 +100,7 @@
     row: Object,
     params: RawMessageInfoFromServerDBRowParams,
   ): RawTextMessageInfo {
-    const rawTextMessageInfo: RawTextMessageInfo = {
+    let rawTextMessageInfo: RawTextMessageInfo = {
       type: messageTypes.TEXT,
       id: row.id.toString(),
       threadID: row.threadID.toString(),
@@ -109,7 +109,7 @@
       text: row.content,
     };
     if (params.localID) {
-      rawTextMessageInfo.localID = params.localID;
+      rawTextMessageInfo = { ...rawTextMessageInfo, localID: params.localID };
     }
     return rawTextMessageInfo;
   },
@@ -117,7 +117,7 @@
   rawMessageInfoFromClientDB(
     clientDBMessageInfo: ClientDBMessageInfo,
   ): RawTextMessageInfo {
-    const rawTextMessageInfo: RawTextMessageInfo = {
+    let rawTextMessageInfo: RawTextMessageInfo = {
       type: messageTypes.TEXT,
       threadID: clientDBMessageInfo.thread,
       time: parseInt(clientDBMessageInfo.time),
@@ -125,10 +125,16 @@
       text: clientDBMessageInfo.content ?? '',
     };
     if (clientDBMessageInfo.local_id) {
-      rawTextMessageInfo.localID = clientDBMessageInfo.local_id;
+      rawTextMessageInfo = {
+        ...rawTextMessageInfo,
+        localID: clientDBMessageInfo.local_id,
+      };
     }
     if (clientDBMessageInfo.id !== clientDBMessageInfo.local_id) {
-      rawTextMessageInfo.id = clientDBMessageInfo.id;
+      rawTextMessageInfo = {
+        ...rawTextMessageInfo,
+        id: clientDBMessageInfo.id,
+      };
     }
     return rawTextMessageInfo;
   },
@@ -137,7 +143,7 @@
     rawMessageInfo: RawTextMessageInfo,
     creator: RelativeUserInfo,
   ): TextMessageInfo {
-    const messageInfo: TextMessageInfo = {
+    let messageInfo: TextMessageInfo = {
       type: messageTypes.TEXT,
       threadID: rawMessageInfo.threadID,
       creator,
@@ -145,10 +151,10 @@
       text: rawMessageInfo.text,
     };
     if (rawMessageInfo.id) {
-      messageInfo.id = rawMessageInfo.id;
+      messageInfo = { ...messageInfo, id: rawMessageInfo.id };
     }
     if (rawMessageInfo.localID) {
-      messageInfo.localID = rawMessageInfo.localID;
+      messageInfo = { ...messageInfo, localID: rawMessageInfo.localID };
     }
     return messageInfo;
   },
diff --git a/lib/types/messages/images.js b/lib/types/messages/images.js
--- a/lib/types/messages/images.js
+++ b/lib/types/messages/images.js
@@ -4,25 +4,25 @@
 import type { RelativeUserInfo } from '../user-types.js';
 
 export type ImagesMessageData = {
-  type: 14,
-  localID?: string, // for optimistic creations. included by new clients
-  threadID: string,
-  creatorID: string,
-  time: number,
-  media: $ReadOnlyArray<Image>,
+  +type: 14,
+  +localID?: string, // for optimistic creations. included by new clients
+  +threadID: string,
+  +creatorID: string,
+  +time: number,
+  +media: $ReadOnlyArray<Image>,
 };
 
 export type RawImagesMessageInfo = {
   ...ImagesMessageData,
-  id?: string, // null if local copy without ID yet
+  +id?: string, // null if local copy without ID yet
 };
 
 export type ImagesMessageInfo = {
-  type: 14,
-  id?: string, // null if local copy without ID yet
-  localID?: string, // for optimistic creations
-  threadID: string,
-  creator: RelativeUserInfo,
-  time: number, // millisecond timestamp
-  media: $ReadOnlyArray<Image>,
+  +type: 14,
+  +id?: string, // null if local copy without ID yet
+  +localID?: string, // for optimistic creations
+  +threadID: string,
+  +creator: RelativeUserInfo,
+  +time: number, // millisecond timestamp
+  +media: $ReadOnlyArray<Image>,
 };
diff --git a/lib/types/messages/media.js b/lib/types/messages/media.js
--- a/lib/types/messages/media.js
+++ b/lib/types/messages/media.js
@@ -4,27 +4,27 @@
 import type { RelativeUserInfo } from '../user-types.js';
 
 export type MediaMessageData = {
-  type: 15,
-  localID?: string, // for optimistic creations. included by new clients
-  threadID: string,
-  creatorID: string,
-  time: number,
-  media: $ReadOnlyArray<Media>,
+  +type: 15,
+  +localID?: string, // for optimistic creations. included by new clients
+  +threadID: string,
+  +creatorID: string,
+  +time: number,
+  +media: $ReadOnlyArray<Media>,
 };
 
 export type RawMediaMessageInfo = {
   ...MediaMessageData,
-  id?: string, // null if local copy without ID yet
+  +id?: string, // null if local copy without ID yet
 };
 
 export type MediaMessageInfo = {
-  type: 15,
-  id?: string, // null if local copy without ID yet
-  localID?: string, // for optimistic creations
-  threadID: string,
-  creator: RelativeUserInfo,
-  time: number, // millisecond timestamp
-  media: $ReadOnlyArray<Media>,
+  +type: 15,
+  +id?: string, // null if local copy without ID yet
+  +localID?: string, // for optimistic creations
+  +threadID: string,
+  +creator: RelativeUserInfo,
+  +time: number, // millisecond timestamp
+  +media: $ReadOnlyArray<Media>,
 };
 
 export type MediaMessageServerDBContent =
diff --git a/lib/types/messages/text.js b/lib/types/messages/text.js
--- a/lib/types/messages/text.js
+++ b/lib/types/messages/text.js
@@ -3,25 +3,25 @@
 import type { RelativeUserInfo } from '../user-types.js';
 
 export type TextMessageData = {
-  type: 0,
-  localID?: string, // for optimistic creations. included by new clients
-  threadID: string,
-  creatorID: string,
-  time: number,
-  text: string,
+  +type: 0,
+  +localID?: string, // for optimistic creations. included by new clients
+  +threadID: string,
+  +creatorID: string,
+  +time: number,
+  +text: string,
 };
 
 export type RawTextMessageInfo = {
   ...TextMessageData,
-  id?: string, // null if local copy without ID yet
+  +id?: string, // null if local copy without ID yet
 };
 
 export type TextMessageInfo = {
-  type: 0,
-  id?: string, // null if local copy without ID yet
-  localID?: string, // for optimistic creations
-  threadID: string,
-  creator: RelativeUserInfo,
-  time: number, // millisecond timestamp
-  text: string,
+  +type: 0,
+  +id?: string, // null if local copy without ID yet
+  +localID?: string, // for optimistic creations
+  +threadID: string,
+  +creator: RelativeUserInfo,
+  +time: number, // millisecond timestamp
+  +text: string,
 };