--- a/toolkit/components/extensions/test/xpcshell/test_ext_permissions.js
+++ b/toolkit/components/extensions/test/xpcshell/test_ext_permissions.js
@@ -261,17 +261,17 @@ add_task(async function test_startup() {
 
   await withHandlingUserInput(extension2, async () => {
     extension2.sendMessage(PERMS2);
     await extension2.awaitMessage("requested");
   });
 
   // Restart everything, and force the permissions store to be
   // re-read on startup
-  ExtensionPermissions._uninit();
+  await ExtensionPermissions._uninit();
   await AddonTestUtils.promiseRestartManager();
   await extension1.awaitStartup();
   await extension2.awaitStartup();
 
   async function checkPermissions(extension, permissions) {
     perms = await extension.awaitMessage("perms");
     let expect = Object.assign({permissions: [], origins: []}, permissions);
     deepEqual(perms, expect, "Extension got correct permissions on startup");