diff --git a/lib/shared/sidebar-utils.js b/lib/shared/sidebar-utils.js
--- a/lib/shared/sidebar-utils.js
+++ b/lib/shared/sidebar-utils.js
@@ -20,7 +20,7 @@
 } from '../types/message-types.js';
 import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-types.js';
 import { threadPermissions } from '../types/thread-permission-types.js';
-import { threadTypes } from '../types/thread-types-enum.js';
+import { threadTypes, threadTypeIsThick } from '../types/thread-types-enum.js';
 import type { LoggedInUserInfo } from '../types/user-types.js';
 import type { GetENSNames } from '../utils/ens-helpers.js';
 import {
@@ -80,7 +80,11 @@
   }
 
   const singleOtherUser = getSingleOtherUser(parentThreadInfo, viewerID);
-  if (parentThreadType === threadTypes.GENESIS_PERSONAL && singleOtherUser) {
+  if (
+    (parentThreadType === threadTypes.GENESIS_PERSONAL ||
+      parentThreadType === threadTypes.PERSONAL) &&
+    singleOtherUser
+  ) {
     const singleOtherUsername = parentThreadInfo.members.find(
       member => member.id === singleOtherUser,
     )?.username;
@@ -107,7 +111,9 @@
 
   return createPendingThread({
     viewerID,
-    threadType: threadTypes.SIDEBAR,
+    threadType: threadTypeIsThick(parentThreadInfo.type)
+      ? threadTypes.THICK_SIDEBAR
+      : threadTypes.SIDEBAR,
     members: [...initialMembers.values()],
     parentThreadInfo,
     threadColor: color,
diff --git a/lib/types/thread-types-enum.js b/lib/types/thread-types-enum.js
--- a/lib/types/thread-types-enum.js
+++ b/lib/types/thread-types-enum.js
@@ -59,6 +59,11 @@
   ...thickThreadTypes,
 });
 
+const thickThreadTypesSet = new Set(Object.values(thickThreadTypes));
+export function threadTypeIsThick(threadType: ThreadType): boolean {
+  return thickThreadTypesSet.has(threadType);
+}
+
 export function assertThinThreadType(threadType: number): ThinThreadType {
   invariant(
     threadType === 3 ||