diff --git a/src/js/background/assignManager.js b/src/js/background/assignManager.js
index 614d480..0962a1d 100644
--- a/src/js/background/assignManager.js
+++ b/src/js/background/assignManager.js
@@ -639,7 +639,7 @@ window.assignManager = {
   },
 
   async _maybeRemoveSiteIsolation(userContextId) {
-    const assignments = await this.storageArea.getByContainer(userContextId);
+    const assignments = await this.storageArea.getAssignedSites(userContextId);
     const hasAssignments = assignments && Object.keys(assignments).length > 0;
     if (hasAssignments) {
       return;