diff --git a/frontend/src/components/execution/values/series/useSpatialIndex.ts b/frontend/src/components/execution/values/series/useSpatialIndex.ts
index e52b0b8..d4862c2 100644
--- a/frontend/src/components/execution/values/series/useSpatialIndex.ts
+++ b/frontend/src/components/execution/values/series/useSpatialIndex.ts
@@ -151,7 +151,7 @@ export function useSpatialIndex(
       hiddenLabels: Set<string>,
     ): NearestResult[] {
       // Find the closest data index by X pixel position
-      const xVal = xScale.invert(pixelX);
+      const xVal = xScale.invert(pixelX) as number;
       let closestDataIdx = 0;
       let closestXDist = Number.POSITIVE_INFINITY;
       for (let i = 0; i < chartData.length; i++) {