diff --git a/app/assets/javascripts/strings.ts b/app/assets/javascripts/strings.ts
index c8a0279536b..98a31cb53e8 100644
--- a/app/assets/javascripts/strings.ts
+++ b/app/assets/javascripts/strings.ts
@@ -49,3 +49,7 @@ export function StringImportError(errorCount: number) {
 
 /** @password_change */
 export const STRING_FAILED_PASSWORD_CHANGE = "There was an error re-encrypting your items. Your password was changed, but not all your items were properly re-encrypted and synced. You should try syncing again. If all else fails, you should restore your notes from backup.";
+
+export const STRING_CONFIRM_APP_QUIT_DURING_UPGRADE =
+  "The encryption upgrade is in progress. You may lose data if you quit the app. " +
+  "Are you sure you want to quit?"
diff --git a/app/assets/javascripts/views/footer/footer_view.ts b/app/assets/javascripts/views/footer/footer_view.ts
index a81d3d43f1e..e4d8c5bcdfd 100644
--- a/app/assets/javascripts/views/footer/footer_view.ts
+++ b/app/assets/javascripts/views/footer/footer_view.ts
@@ -16,7 +16,8 @@ import template from './footer-view.pug';
 import { AppStateEvent, EventSource } from '@/ui_models/app_state';
 import {
   STRING_GENERIC_SYNC_ERROR,
-  STRING_NEW_UPDATE_READY
+  STRING_NEW_UPDATE_READY,
+  STRING_CONFIRM_APP_QUIT_DURING_UPGRADE
 } from '@/strings';
 import { PureViewCtrl } from '@Views/abstract/pure_view_ctrl';
 import { ComponentMutator } from '@node_modules/snjs/dist/@types/models';
@@ -298,8 +299,14 @@ class FooterViewCtrl extends PureViewCtrl {
     this.offline = this.application!.noAccount();
   }
 
-  openSecurityUpdate() {
-    this.application!.performProtocolUpgrade();
+  async openSecurityUpdate() {
+    const onBeforeUnload = window.onbeforeunload;
+    try {
+      window.onbeforeunload = () => STRING_CONFIRM_APP_QUIT_DURING_UPGRADE;
+      await this.application!.performProtocolUpgrade();
+    } finally {
+      window.onbeforeunload = onBeforeUnload;
+    }
   }
 
   findErrors() {