diff --git a/app/components/post_list/combined_user_activity/combined_user_activity.tsx b/app/components/post_list/combined_user_activity/combined_user_activity.tsx
index c176b02905f..43eb5381ad8 100644
--- a/app/components/post_list/combined_user_activity/combined_user_activity.tsx
+++ b/app/components/post_list/combined_user_activity/combined_user_activity.tsx
@@ -116,12 +116,12 @@ const CombinedUserActivity = ({
         }
     }, [post, canDelete, isTablet, intl, location]);
 
-    const renderMessage = (postType: string, userIds: string[], actorId: string) => {
+    const renderMessage = (postType: string, userIds: string[], actorId?: string) => {
         if (!post) {
             return null;
         }
         let actor = '';
-        if (secureGetFromRecord(usernamesById, actorId)) {
+        if (actorId && secureGetFromRecord(usernamesById, actorId)) {
             actor = `@${usernamesById[actorId]}`;
         }
 
diff --git a/app/utils/post_list/index.ts b/app/utils/post_list/index.ts
index 76f6e2a212f..d2a8cb514c7 100644
--- a/app/utils/post_list/index.ts
+++ b/app/utils/post_list/index.ts
@@ -389,7 +389,7 @@ export function shouldFilterJoinLeavePost(post: PostModel, showJoinLeave: boolea
 }
 
 export type MessageData = {
-    actorId: string;
+    actorId?: string;
     postType: string;
     userIds: string[];
 }
@@ -399,7 +399,7 @@ function isMessageData(v: unknown): v is MessageData {
         return false;
     }
 
-    if (!('actorId' in v) || typeof v.actorId !== 'string') {
+    if (('actorId' in v) && typeof v.actorId !== 'string') {
         return false;
     }