diff --git a/web/components/ChartCard/usePlot.ts b/web/components/ChartCard/usePlot.ts
index a84ea6b..b0eb7a8 100644
--- a/web/components/ChartCard/usePlot.ts
+++ b/web/components/ChartCard/usePlot.ts
@@ -57,11 +57,11 @@ export function usePlot(
 
       // Defer mouseleave — prevents React hydration events firing before lastIdxRef set
       requestAnimationFrame(() => {
-        plot.over.addEventListener('mouseleave', () => {
+        plot.over.onmouseleave = () => {
           const p = plotRef.current;
           if (!p) return;
           p.setCursor({ left: idxToPixel(p, lastIdxRef.current), top: -10 });
-        });
+        };
       });
     }
     // deps is intentionally dynamic — passed by parent to allow external rebuild triggers