diff --git a/addons/web/static/src/js/core.js b/addons/web/static/src/js/core.js
index 31a94756246..4bc86dce5ef 100644
--- a/addons/web/static/src/js/core.js
+++ b/addons/web/static/src/js/core.js
@@ -445,7 +445,8 @@ instance.web.Session.include( /** @lends instance.web.Session# */{
                 try {
                     if (options.error) {
                         var body = this.contentDocument.body;
-                        var node = body.childNodes[1] || body.childNodes[0];
+                        var nodes = body.children.length === 0 ? body.childNodes : body.children;
+                        var node = nodes[1] || nodes[0];
                         options.error(JSON.parse(node.textContent));
                     }
                 } finally {