diff --git a/lib/IHP/static/helpers.js b/lib/IHP/static/helpers.js
index 248b0447d..66fb2a97e 100644
--- a/lib/IHP/static/helpers.js
+++ b/lib/IHP/static/helpers.js
@@ -278,7 +278,7 @@ window.submitForm = function (form, possibleClickedButton) {
             // of full urls like `http://example.com/Projects`
             var url = new URL(formAction, document.baseURI);
             for (var pair of formData.entries()) {
-                url.searchParams.set(pair[0], pair[1]);
+                url.searchParams.append(pair[0], pair[1]);
             }
 
             request.open(formMethod, url.toString(), true);