diff --git a/cast/templates/cast/image/image.html b/cast/templates/cast/image/image.html
index c565bf2f..6ffc4471 100644
--- a/cast/templates/cast/image/image.html
+++ b/cast/templates/cast/image/image.html
@@ -4,14 +4,14 @@
     <source
       srcset="{{ value.thumbnail.srcset.avif }}"
       type="image/avif"
-      sizes="{{ value.thumbnail.sizes }}"
+      sizes="(max-width: 600px) 555px, {{ value.thumbnail.sizes }}"
     >
     <img
       class="cast-image"
       alt="{{ value.default_alt_text }}"
       src="{{ value.thumbnail.src.jpeg }}"
       srcset="{{ value.thumbnail.srcset.jpeg }}"
-      sizes="{{ value.thumbnail.sizes }}"
+      sizes="(max-width: 600px) 555px {{ value.thumbnail.sizes }}"
       width="{{ value.thumbnail.width }}"
       height="{{ value.thumbnail.height }}"
     >