diff --git a/frontend/app/trees/[id]/tree/page.tsx b/frontend/app/trees/[id]/tree/page.tsx
index 2baeef1..02b3c35 100644
--- a/frontend/app/trees/[id]/tree/page.tsx
+++ b/frontend/app/trees/[id]/tree/page.tsx
@@ -315,8 +315,12 @@ export default function TreePage() {
         try {
           const rect = svg.getBoundingClientRect();
           const scale = handlers.getCurrentZoom ? handlers.getCurrentZoom(svg).k : 1;
+          // family-chart's cardToMiddle scales datum.x by the zoom but NOT
+          // datum.y (a library bug), so vertical centering is only correct at
+          // scale 1 and drifts by datum.y·(k−1) otherwise — landing "below the
+          // tree". Pre-multiply y by the scale to cancel the missing ·k.
           handlers.cardToMiddle({
-            datum: xy,
+            datum: { x: xy.x, y: xy.y * scale },
             svg,
             svg_dim: { width: rect.width, height: rect.height },
             scale,