diff --git a/static/canvas-renderer.js b/static/canvas-renderer.js
index dfb00ec..5e5d25a 100644
--- a/static/canvas-renderer.js
+++ b/static/canvas-renderer.js
@@ -54,6 +54,7 @@ class CanvasRenderer extends HTMLElement {
     }
 
     getWindowSize() {
+        if (this.width == null || this.height == null) return { width: 0, height: 0 };
         return {
             width: this.width,
             height: this.height,