diff --git a/lib/shared/dm-ops/change-thread-settings-spec.js b/lib/shared/dm-ops/change-thread-settings-spec.js
--- a/lib/shared/dm-ops/change-thread-settings-spec.js
+++ b/lib/shared/dm-ops/change-thread-settings-spec.js
@@ -15,10 +15,7 @@
 import type { RawMessageInfo } from '../../types/message-types';
 import { messageTypes } from '../../types/message-types-enum.js';
 import type { ChangeSettingsMessageData } from '../../types/messages/change-settings.js';
-import type {
-  RawThreadInfo,
-  ThickRawThreadInfo,
-} from '../../types/minimally-encoded-thread-permissions-types.js';
+import type { RawThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import { updateTypes } from '../../types/update-types-enum.js';
 import type { ClientUpdateInfo } from '../../types/update-types.js';
 import { blobHashFromBlobServiceURI } from '../../utils/blob-service.js';
@@ -74,7 +71,10 @@
   } = {};
 
   const { avatar: avatarObject, ...rest } = threadInfoUpdate;
-  let normalizedThreadInfoUpdate;
+  let normalizedThreadInfoUpdate: $ReadOnly<{
+    ...DMThreadSettingsChanges,
+    avatar?: string,
+  }>;
   if (avatarObject) {
     normalizedThreadInfoUpdate = {
       ...rest,
@@ -154,7 +154,7 @@
         ({ rawMessageInfo }) => rawMessageInfo,
       );
 
-      let threadInfoToUpdate: ThickRawThreadInfo = threadInfo;
+      let threadInfoToUpdate = { ...threadInfo };
       for (const fieldName of Object.keys(threadInfoUpdate)) {
         const timestamp = threadInfoToUpdate.timestamps[fieldName];
         if (timestamp < time) {