diff --git a/ui/src/components/FoldCurtain.tsx b/ui/src/components/FoldCurtain.tsx
index 4cdbfd27c22..a6370b26ce1 100644
--- a/ui/src/components/FoldCurtain.tsx
+++ b/ui/src/components/FoldCurtain.tsx
@@ -80,6 +80,7 @@ export function FoldCurtain({
       setHasMeasured(true);
     };
     measure();
+    if (typeof ResizeObserver === "undefined") return;
     const observer = new ResizeObserver(measure);
     observer.observe(el);
     return () => observer.disconnect();