diff --git a/apps/client/src/components/tab_manager.ts b/apps/client/src/components/tab_manager.ts
index 47305b2a5..6b0a48b08 100644
--- a/apps/client/src/components/tab_manager.ts
+++ b/apps/client/src/components/tab_manager.ts
@@ -138,7 +138,7 @@ export default class TabManager extends Component {
             // Save window contents
             if (currentWin) {
                 currentWin.createdAt = Date.now();
-                currentWin.closedAt = null;
+                currentWin.closedAt = 0;
                 currentWin.contexts = filteredNoteContexts;
             } else {
                 // Filter out the oldest entry (excluding the main window)