diff --git a/ext/bg/js/settings-dictionaries.js b/ext/bg/js/settings-dictionaries.js
index c40648e0..786fcbd5 100644
--- a/ext/bg/js/settings-dictionaries.js
+++ b/ext/bg/js/settings-dictionaries.js
@@ -222,7 +222,10 @@ class SettingsDictionaryEntryUI {
         const progressBar = this.content.querySelector('.progress-bar');
         this.isDeleting = true;
 
+        const prevention = new PageExitPrevention();
         try {
+            prevention.start();
+
             const onProgress = ({processed, count, storeCount, storesProcesed}) => {
                 let percent = 0.0;
                 if (count > 0 && storesProcesed > 0) {
@@ -235,6 +238,7 @@ class SettingsDictionaryEntryUI {
         } catch (e) {
             dictionaryErrorsShow([e]);
         } finally {
+            prevention.end();
             this.isDeleting = false;
             progress.hidden = true;
 
@@ -479,7 +483,10 @@ async function onDictionaryPurge(e) {
     const dictProgress = document.querySelector('#dict-purge');
     dictProgress.hidden = false;
 
+    const prevention = new PageExitPrevention();
+
     try {
+        prevention.start();
         dictionaryErrorsShow(null);
         dictionarySpinnerShow(true);
 
@@ -496,6 +503,8 @@ async function onDictionaryPurge(e) {
     } catch (err) {
         dictionaryErrorsShow([err]);
     } finally {
+        prevention.end();
+
         dictionarySpinnerShow(false);
 
         dictControls.show();
@@ -513,7 +522,10 @@ async function onDictionaryImport(e) {
     const dictProgress = $('#dict-import-progress').show();
     const dictImportInfo = document.querySelector('#dict-import-info');
 
+    const prevention = new PageExitPrevention();
+
     try {
+        prevention.start();
         dictionaryErrorsShow(null);
         dictionarySpinnerShow(true);
 
@@ -559,6 +571,7 @@ async function onDictionaryImport(e) {
     } catch (err) {
         dictionaryErrorsShow([err]);
     } finally {
+        prevention.end();
         dictionarySpinnerShow(false);
 
         dictImportInfo.hidden = false;
diff --git a/ext/bg/js/settings.js b/ext/bg/js/settings.js
index e4446851..d4b1549e 100644
--- a/ext/bg/js/settings.js
+++ b/ext/bg/js/settings.js
@@ -211,6 +211,52 @@ async function onReady() {
 $(document).ready(utilAsync(onReady));
 
 
+/*
+ * Page exit prevention
+ */
+
+class PageExitPrevention {
+    constructor() {
+    }
+
+    start() {
+        PageExitPrevention._addInstance(this);
+    }
+
+    end() {
+        PageExitPrevention._removeInstance(this);
+    }
+
+    static _addInstance(instance) {
+        const size = PageExitPrevention._instances.size;
+        PageExitPrevention._instances.set(instance, true);
+        if (size === 0) {
+            window.addEventListener('beforeunload', PageExitPrevention._onBeforeUnload);
+        }
+    }
+
+    static _removeInstance(instance) {
+        if (
+            PageExitPrevention._instances.delete(instance) &&
+            PageExitPrevention._instances.size === 0
+        ) {
+            window.removeEventListener('beforeunload', PageExitPrevention._onBeforeUnload);
+        }
+    }
+
+    static _onBeforeUnload(e) {
+        if (PageExitPrevention._instances.size === 0) {
+            return;
+        }
+
+        e.preventDefault();
+        e.returnValue = '';
+        return '';
+    }
+}
+PageExitPrevention._instances = new Map();
+
+
 /*
  * Appearance
  */