diff --git a/lib/shared/updates/update-thread-read-status-spec.js b/lib/shared/updates/update-thread-read-status-spec.js
--- a/lib/shared/updates/update-thread-read-status-spec.js
+++ b/lib/shared/updates/update-thread-read-status-spec.js
@@ -3,10 +3,7 @@
 import t from 'tcomb';
 
 import type { UpdateSpec } from './update-spec.js';
-import type {
-  LegacyRawThreadInfo,
-  LegacyRawThreadInfos,
-} from '../../types/thread-types.js';
+import type { RawThreadInfos } from '../../types/thread-types.js';
 import { updateTypes } from '../../types/update-types-enum.js';
 import type {
   ThreadReadStatusUpdateInfo,
@@ -21,24 +18,35 @@
   ThreadReadStatusUpdateData,
 > = Object.freeze({
   generateOpsForThreadUpdates(
-    storeThreadInfos: LegacyRawThreadInfos,
+    storeThreadInfos: RawThreadInfos,
     update: ThreadReadStatusUpdateInfo,
   ) {
-    const storeThreadInfo: ?LegacyRawThreadInfo =
-      storeThreadInfos[update.threadID];
     if (
-      !storeThreadInfo ||
-      storeThreadInfo.currentUser.unread === update.unread
+      !storeThreadInfos[update.threadID] ||
+      storeThreadInfos[update.threadID].currentUser.unread === update.unread
     ) {
       return null;
     }
-    const updatedThread = {
-      ...storeThreadInfo,
-      currentUser: {
-        ...storeThreadInfo.currentUser,
-        unread: update.unread,
-      },
-    };
+    const storeThreadInfo = storeThreadInfos[update.threadID];
+
+    let updatedThread;
+    if (storeThreadInfo.minimallyEncoded) {
+      updatedThread = {
+        ...storeThreadInfo,
+        currentUser: {
+          ...storeThreadInfo.currentUser,
+          unread: update.unread,
+        },
+      };
+    } else {
+      updatedThread = {
+        ...storeThreadInfo,
+        currentUser: {
+          ...storeThreadInfo.currentUser,
+          unread: update.unread,
+        },
+      };
+    }
     return [
       {
         type: 'replace',