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
@@ -269,6 +269,9 @@
   return `pending/${pendingThreadTypeString}${pendingThreadKey}`;
 }
 
+const locallyUniqueThreadIDRegex =
+  'pending/(type[0-9]+/[0-9]+(\\+[0-9]+)*|sidebar/[0-9]+)';
+
 type CreatePendingThreadArgs = {
   +viewerID: string,
   +threadType: ThreadType,
@@ -1381,6 +1384,7 @@
   threadIsPending,
   getSingleOtherUser,
   getLocallyUniqueThreadID,
+  locallyUniqueThreadIDRegex,
   createPendingThread,
   createPendingThreadItem,
   createPendingSidebar,
diff --git a/lib/utils/url-utils.js b/lib/utils/url-utils.js
--- a/lib/utils/url-utils.js
+++ b/lib/utils/url-utils.js
@@ -2,6 +2,8 @@
 
 import urlParseLax from 'url-parse-lax';
 
+import { locallyUniqueThreadIDRegex } from '../shared/thread-utils';
+
 export type URLInfo = {
   +year?: number,
   +month?: number, // 1-indexed
@@ -14,6 +16,8 @@
   ...
 };
 
+// We use groups to capture parts of the URL and any changes
+// to regexes must be reflected in infoFromURL.
 const yearRegex = new RegExp('(/|^)year/([0-9]+)(/|$)', 'i');
 const monthRegex = new RegExp('(/|^)month/([0-9]+)(/|$)', 'i');
 const threadRegex = new RegExp('(/|^)thread/([0-9]+)(/|$)', 'i');
@@ -23,6 +27,10 @@
 const appsRegex = new RegExp('(/|^)apps(/|$)', 'i');
 const accountSettingsRegex = new RegExp('(/|^)settings/account(/|$)', 'i');
 const dangerZoneRegex = new RegExp('(/|^)settings/danger-zone(/|$)', 'i');
+const threadPendingRegex = new RegExp(
+  `(/|^)thread/(${locallyUniqueThreadIDRegex})(/|$)`,
+  'i',
+);
 
 function infoFromURL(url: string): URLInfo {
   const yearMatches = yearRegex.exec(url);
@@ -34,6 +42,7 @@
   const appsTest = appsRegex.test(url);
   const accountSettingsTest = accountSettingsRegex.test(url);
   const dangerZoneTest = dangerZoneRegex.test(url);
+  const threadPendingMatches = threadPendingRegex.exec(url);
 
   const returnObj = {};
   if (yearMatches) {
@@ -49,6 +58,9 @@
   if (threadMatches) {
     returnObj.thread = threadMatches[2];
   }
+  if (threadPendingMatches) {
+    returnObj.thread = threadPendingMatches[2];
+  }
   if (verifyMatches) {
     returnObj.verify = verifyMatches[2];
   }