diff --git a/lib/shared/thread-utils.js b/lib/shared/thread-utils.js
--- a/lib/shared/thread-utils.js
+++ b/lib/shared/thread-utils.js
@@ -111,7 +111,11 @@
 import { userSurfacedPermissionsFromRolePermissions } from '../utils/role-utils.js';
 import { usingOlmViaTunnelbrokerForDMs } from '../utils/services-utils.js';
 import { firstLine } from '../utils/string-utils.js';
-import { pendingThreadIDRegex } from '../utils/validation-utils.js';
+import {
+  pendingThreadIDRegex,
+  pendingThickSidebarURLPrefix,
+  pendingSidebarURLPrefix,
+} from '../utils/validation-utils.js';
 
 function threadHasPermission(
   threadInfo: ?(ThreadInfo | LegacyRawThreadInfo | RawThreadInfo),
@@ -373,7 +377,10 @@
 }
 
 function threadIsPendingSidebar(threadID: ?string): boolean {
-  return !!threadID?.startsWith('pending/sidebar/');
+  return (
+    !!threadID?.startsWith(`pending/${pendingSidebarURLPrefix}/`) ||
+    !!threadID?.startsWith(`pending/${pendingThickSidebarURLPrefix}`)
+  );
 }
 
 function getSingleOtherUser(
@@ -397,9 +404,9 @@
 ): string {
   let pendingThreadKey;
   if (sourceMessageID && threadTypeIsThick(threadType)) {
-    pendingThreadKey = `dm_sidebar/${sourceMessageID}`;
+    pendingThreadKey = `${pendingThickSidebarURLPrefix}/${sourceMessageID}`;
   } else if (sourceMessageID) {
-    pendingThreadKey = `sidebar/${sourceMessageID}`;
+    pendingThreadKey = `${pendingSidebarURLPrefix}/${sourceMessageID}`;
   } else {
     pendingThreadKey = [...memberIDs].sort().join('+');
   }
@@ -425,16 +432,17 @@
 
   const [threadTypeString, threadKey] = pendingThreadIDMatches[1].split('/');
   let threadType;
-  if (threadTypeString === 'dm_sidebar') {
+  if (threadTypeString === pendingThickSidebarURLPrefix) {
     threadType = threadTypes.THICK_SIDEBAR;
-  } else if (threadTypeString === 'sidebar') {
+  } else if (threadTypeString === pendingSidebarURLPrefix) {
     threadType = threadTypes.SIDEBAR;
   } else {
     threadType = assertThreadType(Number(threadTypeString.replace('type', '')));
   }
 
   const threadTypeStringIsSidebar =
-    threadTypeString === 'sidebar' || threadTypeString === 'dm_sidebar';
+    threadTypeString === pendingSidebarURLPrefix ||
+    threadTypeString === pendingThickSidebarURLPrefix;
   const memberIDs = threadTypeStringIsSidebar ? [] : threadKey.split('+');
   const sourceMessageID = threadTypeStringIsSidebar ? threadKey : null;
   return {
diff --git a/lib/shared/thread-utils.test.js b/lib/shared/thread-utils.test.js
--- a/lib/shared/thread-utils.test.js
+++ b/lib/shared/thread-utils.test.js
@@ -4,6 +4,7 @@
   parsePendingThreadID,
   threadInfoFromRawThreadInfo,
   getPendingThreadID,
+  threadIsPendingSidebar,
 } from './thread-utils.js';
 import { threadInfoValidator } from '../permissions/minimally-encoded-thread-permissions-validators.js';
 import type { RawThreadInfo } from '../types/minimally-encoded-thread-permissions-types.js';
@@ -213,3 +214,28 @@
     ).toStrictEqual('pending/dm_sidebar/12345');
   });
 });
+
+describe('threadIsPendingSidebar', () => {
+  it('should correctly check if sidebar is pending', () => {
+    const thinPendingSidebarID = getPendingThreadID(
+      threadTypes.SIDEBAR,
+      [],
+      '12345',
+    );
+    const thickPendingSidebarID = getPendingThreadID(
+      threadTypes.THICK_SIDEBAR,
+      [],
+      '12345',
+    );
+    const nonSidebarPendinThreadID = getPendingThreadID(
+      threadTypes.PERSONAL,
+      [],
+    );
+
+    expect(threadIsPendingSidebar(thinPendingSidebarID)).toStrictEqual(true);
+    expect(threadIsPendingSidebar(thickPendingSidebarID)).toStrictEqual(true);
+    expect(threadIsPendingSidebar(nonSidebarPendinThreadID)).toStrictEqual(
+      false,
+    );
+  });
+});
diff --git a/lib/utils/validation-utils.js b/lib/utils/validation-utils.js
--- a/lib/utils/validation-utils.js
+++ b/lib/utils/validation-utils.js
@@ -112,7 +112,9 @@
   '[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}';
 const idSchemaRegex = `(?:(?:[0-9]+|${uuidRegex})\\|)?(?:[0-9]+|${uuidRegex})`;
 
-const pendingThreadIDRegex = `pending/(type[0-9]+/[0-9]+(\\+[0-9]+)*|(sidebar|dm_sidebar)/${idSchemaRegex})`;
+const pendingSidebarURLPrefix = 'sidebar';
+const pendingThickSidebarURLPrefix = 'dm_sidebar';
+const pendingThreadIDRegex = `pending/(type[0-9]+/[0-9]+(\\+[0-9]+)*|(${pendingSidebarURLPrefix}|${pendingThickSidebarURLPrefix})/${idSchemaRegex})`;
 const thickThreadIDRegex: RegExp = new RegExp(`^${uuidRegex}$`);
 
 const chatNameMaxLength = 191;
@@ -146,6 +148,8 @@
   assertWithValidator,
   ashoatKeyserverID,
   idSchemaRegex,
+  pendingSidebarURLPrefix,
+  pendingThickSidebarURLPrefix,
   pendingThreadIDRegex,
   thickThreadIDRegex,
   validChatNameRegex,