diff --git a/src/banner/banner-manager.mjs b/src/banner/banner-manager.mjs
index 712ba2c..8632167 100644
--- a/src/banner/banner-manager.mjs
+++ b/src/banner/banner-manager.mjs
@@ -32,8 +32,8 @@ export class BannerManager {
         this.STATE = State;
     }
 
-    addExternalBanner(element) {
-        element = getHtmlElement(element);
+    addExternalBanner(element, refWindow = window) {
+        element = getHtmlElement(element, refWindow);
 
         element.setAttribute('data-amp-attached', '');
 
@@ -49,12 +49,12 @@ export class BannerManager {
         return banner;
     }
 
-    addManagedBanner(element, position, resources = {}, options = {}) {
+    addManagedBanner(element, position, resources = {}, options = {}, refWindow = window) {
         if (null === this.#bannerRenderer) {
             throw new Error(`Unable to add managed banner, renderer is not provided.`);
         }
 
-        element = getHtmlElement(element);
+        element = getHtmlElement(element, refWindow);
 
         element.setAttribute('data-amp-attached', '');
 
@@ -75,8 +75,8 @@ export class BannerManager {
     }
 
     addEmbedBanner(element, iframe, position, options) {
-        element = getHtmlElement(element);
-        iframe = getHtmlElement(iframe);
+        element = getHtmlElement(element, window);
+        iframe = getHtmlElement(iframe, window);
 
         element.setAttribute('data-amp-attached', '');
 
diff --git a/src/client/standard/client.mjs b/src/client/standard/client.mjs
index 9ba5e71..72dd407 100644
--- a/src/client/standard/client.mjs
+++ b/src/client/standard/client.mjs
@@ -159,8 +159,8 @@ export class Client {
         return this.#gateway;
     }
 
-    createBanner(element, position, resources = {}, options = {}, mode = 'managed') {
-        element = getHtmlElement(element);
+    createBanner(element, position, resources = {}, options = {}, mode = 'managed', refWindow = window) {
+        element = getHtmlElement(element, refWindow);
 
         if ('embed' === mode) {
             const iframe = this.#createIframe(element, position, resources, options);
@@ -172,14 +172,14 @@ export class Client {
             return banner;
         }
 
-        return this.#bannerManager.addManagedBanner(element, position, resources, options);
+        return this.#bannerManager.addManagedBanner(element, position, resources, options, refWindow);
     }
 
     closeBanner(bannerId) {
         this.#closingManager.closeBanner(bannerId);
     }
 
-    attachBanners(snippet = document) {
+    attachBanners(snippet = document, refWindow = window) {
         const elements = snippet.querySelectorAll('[data-amp-banner]:not([data-amp-attached])');
 
         for (let element of elements) {
@@ -194,13 +194,13 @@ export class Client {
             let banner;
 
             if ('ampBannerExternal' in element.dataset) {
-                banner = this.#bannerManager.addExternalBanner(element);
+                banner = this.#bannerManager.addExternalBanner(element, refWindow);
             } else {
                 const resources = AttributesParser.parseResources(element);
                 const options = AttributesParser.parseOptions(element);
                 const mode = element.dataset.ampMode || 'managed';
 
-                banner = this.createBanner(element, position, resources, options, mode);
+                banner = this.createBanner(element, position, resources, options, mode, refWindow);
             }
 
             this.#eventBus.dispatch(this.EVENTS.ON_BANNER_ATTACHED, { banner });
diff --git a/src/utils/dom-helpers.mjs b/src/utils/dom-helpers.mjs
index b7eeff4..aee23cc 100644
--- a/src/utils/dom-helpers.mjs
+++ b/src/utils/dom-helpers.mjs
@@ -1,5 +1,11 @@
-export function getHtmlElement(el) {
-    if (el instanceof HTMLElement) {
+/**
+ *
+ * @param {string|HTMLElement} el
+ * @param {Window} refWindow
+ * @returns {HTMLElement}
+ */
+export function getHtmlElement(el, refWindow) {
+    if (el instanceof refWindow.HTMLElement) {
         return el;
     }
 
@@ -15,7 +21,7 @@ export function getHtmlElement(el) {
         htmlEl = document.querySelector(el);
     }
 
-    if (!(htmlEl instanceof HTMLElement)) {
+    if (!(htmlEl instanceof refWindow.HTMLElement)) {
         throw new TypeError('Selector ' + el + ' is invalid.');
     }