diff --git a/ui/button.js b/ui/button.js
index 14add61..04298bc 100644
--- a/ui/button.js
+++ b/ui/button.js
@@ -1,7 +1,7 @@
 class Button {
     constructor(image) {
         this.element = document.createElement("button");
-        this.element.add("shadow");
+        this.element.classList.add("shadow");
         this.element.style.backgroundImage = "url(images/" + image + ".svg)";
         this._boundClick = this._onClick.bind(this);
         this.element.addEventListener("click", this._boundClick, false);