diff --git a/lib/reducers/message-reducer.js b/lib/reducers/message-reducer.js
--- a/lib/reducers/message-reducer.js
+++ b/lib/reducers/message-reducer.js
@@ -367,8 +367,7 @@
   );
   const orderedNewMessageInfos = _flow(
     _map((messageInfo: RawMessageInfo) => {
-      const { id: inputID } = messageInfo;
-      invariant(inputID, 'new messageInfos should have serverID');
+      const inputID = messageID(messageInfo);
       invariant(
         !threadIsPending(messageInfo.threadID),
         'new messageInfos should have realized thread id',
@@ -383,6 +382,9 @@
         const currentLocalMessageInfo = inputLocalID
           ? updatedMessageStore.messages[inputLocalID]
           : null;
+        const isThick = threadTypeIsThick(
+          threadInfos[messageInfo.threadID].type,
+        );
         if (currentMessageInfo && currentMessageInfo.localID) {
           // If the client already has a RawMessageInfo with this serverID, keep
           // any localID associated with the existing one. This is because we
@@ -428,10 +430,13 @@
               localID: currentLocalMessageInfo.localID,
             }: RawImagesMessageInfo);
           }
-        } else {
+        } else if (!isThick) {
           // If neither the serverID nor the localID from the delivered
           // RawMessageInfo exists in the client store, then this message is
           // brand new to us. Ignore any localID provided by the server.
+          // It is also possible that this is a failed thick thread message,
+          // in which case we shouldn't remove the localID, because this
+          // message doesn't have an ID yet.
           // (The conditional below is for Flow)
           const { localID, ...rest } = messageInfo;
           if (rest.type === messageTypes.TEXT) {