diff --git a/src/GraphicsSystem/CalcEdgeSealing.ts b/src/GraphicsSystem/CalcEdgeSealing.ts
index 8e467c98e..fbfc05cc1 100644
--- a/src/GraphicsSystem/CalcEdgeSealing.ts
+++ b/src/GraphicsSystem/CalcEdgeSealing.ts
@@ -179,7 +179,7 @@ export function GetBoardSealingCurves(br: Board)
     else
     {
         let cu = br.ContourCurve as Polyline;
-        let index = cu.GetParamAtPoint(new Vector3());
+        let index = Math.round(cu.GetParamAtPoint(new Vector3()));
         while (cus.length < 4)
         {
             cus.push(cu.GetCurveAtIndex(index));