diff --git a/docs/index.rst b/docs/index.rst
index 06456ac9..c9112ef0 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -84,7 +84,7 @@ As an example, consider the design of a tea cup:
 .. raw:: html
 
     <script type="module" src="https://unpkg.com/@google/model-viewer/dist/model-viewer.min.js"></script>
-    <model-viewer src="_static/tea_cup.glb" alt="A tea cup modelled in build123d" auto-rotate camera-controls style="width: 100%"></model-viewer>
+    <model-viewer src="_static/tea_cup.glb" alt="A tea cup modelled in build123d" auto-rotate camera-controls style="width: 100%; aspect-ratio: 1 / 1;"></model-viewer>
 
 .. image:: tea_cup.png
   :align: center