diff --git a/addons/web_editor/static/src/js/wysiwyg/wysiwyg_iframe.js b/addons/web_editor/static/src/js/wysiwyg/wysiwyg_iframe.js
index f913b0340ca..3707d987b7e 100644
--- a/addons/web_editor/static/src/js/wysiwyg/wysiwyg_iframe.js
+++ b/addons/web_editor/static/src/js/wysiwyg/wysiwyg_iframe.js
@@ -154,7 +154,7 @@ Wysiwyg.include({
                 self.$iframe[0].contentWindow.document
                     .open("text/html", "replace")
                     .write(`<!DOCTYPE html><html${
-                        self.options.iframeHtmlClass ? ` class="${self.options.iframeHtmlClass}"` : ''
+                        self.options.iframeHtmlClass ? ' class="' + self.options.iframeHtmlClass +'"' : ''
                     }>${iframeContent}</html>`);
             });
             self.options.document = self.$iframe[0].contentWindow.document;