diff --git a/frontend/app/common/constants.config.test.ts b/frontend/app/common/constants.config.test.ts
new file mode 100644
index 00000000..e928d1e5
--- /dev/null
+++ b/frontend/app/common/constants.config.test.ts
@@ -0,0 +1,47 @@
+import { getBaseUrl } from './constants.config';
+
+describe('constants.config', () => {
+  let host: string;
+  let consoleErrorSpy: jest.SpyInstance;
+
+  beforeAll(() => {
+    host = window.remark_config.host!;
+  });
+  beforeEach(() => {
+    consoleErrorSpy = jest.spyOn(console, 'error').mockImplementationOnce(jest.fn());
+  });
+  afterEach(() => {
+    consoleErrorSpy.mockClear();
+    window.remark_config.host = host;
+  });
+
+  describe('BASE_URL validation', () => {
+    beforeEach(() => {
+      Object.defineProperty(window, 'location', {
+        value: { protocol: 'https:' },
+        writable: true,
+      });
+    });
+    it('should throw error if host is not defined', () => {
+      window.remark_config.host = undefined;
+      expect(() => getBaseUrl()).toThrowError(`Remark42: remark_config.host wasn't configured.`);
+    });
+    it('should show mismatch error', () => {
+      expect(getBaseUrl()).toBe('http://test.com');
+      expect(consoleErrorSpy).toHaveBeenCalledTimes(1);
+      expect(consoleErrorSpy).toHaveBeenCalledWith('Remark42: Protocol mismatch.');
+    });
+    it('should throw error when BASE_URL has wrong protocol', () => {
+      window.remark_config.host = 'data:application/json;base64';
+      expect(() => getBaseUrl()).toThrowError('Remark42: Invalid host URL.');
+      expect(consoleErrorSpy).toHaveBeenCalledTimes(2);
+      expect(consoleErrorSpy).toHaveBeenNthCalledWith(1, 'Remark42: Protocol mismatch.');
+      expect(consoleErrorSpy).toHaveBeenNthCalledWith(2, 'Remark42: Wrong protocol in host URL.');
+    });
+    it('should throw error when BASE_URL is invalid', () => {
+      window.remark_config.host = 'asfasdfa!asds';
+      expect(() => getBaseUrl()).toThrowError('Remark42: Invalid host URL.');
+      expect(consoleErrorSpy).toHaveBeenCalledTimes(0);
+    });
+  });
+});
diff --git a/frontend/app/common/constants.config.ts b/frontend/app/common/constants.config.ts
index 8f5fb504..c84658e0 100644
--- a/frontend/app/common/constants.config.ts
+++ b/frontend/app/common/constants.config.ts
@@ -1,4 +1,30 @@
-export const BASE_URL = window.remark_config.host || process.env.REMARK_URL!;
 export const NODE_ID = process.env.REMARK_NODE!;
 export const API_BASE = '/api/v1';
 export const COMMENT_NODE_CLASSNAME_PREFIX = 'remark42__comment-';
+export const BASE_URL = getBaseUrl();
+
+export function getBaseUrl() {
+  const baseUrl = window.remark_config.host ?? process.env.REMARK_URL;
+
+  if (!baseUrl) {
+    throw new Error(`Remark42: remark_config.host wasn't configured.`);
+  }
+
+  // Validate host
+  try {
+    const { protocol } = new URL(baseUrl);
+    // Show error if protocol of iframe doesn't match protocol of current page
+    if (protocol !== window.location.protocol) {
+      console.error('Remark42: Protocol mismatch.');
+    }
+    // Check if host has valid protocol and prevent XSS vurnuality
+    if (!protocol.startsWith('http')) {
+      console.error('Remark42: Wrong protocol in host URL.');
+      throw new Error();
+    }
+  } catch (e) {
+    throw new Error('Remark42: Invalid host URL.');
+  }
+
+  return baseUrl;
+}
diff --git a/frontend/app/typings/global.d.ts b/frontend/app/typings/global.d.ts
index 41186937..0e09286a 100644
--- a/frontend/app/typings/global.d.ts
+++ b/frontend/app/typings/global.d.ts
@@ -2,7 +2,7 @@ import 'jest-fetch-mock';
 import type { Theme } from 'common/types';
 
 type RemarkConfig = {
-  host: string;
+  host?: string;
   site_id: string;
   url?: string;
   max_shown_comments?: number;