diff --git a/src/graphics/slope/SlopeAssistant.ts b/src/graphics/slope/SlopeAssistant.ts
index 95427f6..98b220e 100644
--- a/src/graphics/slope/SlopeAssistant.ts
+++ b/src/graphics/slope/SlopeAssistant.ts
@@ -65,11 +65,17 @@ export class SlopeDraw extends GraphicDrawAssistant<SlopeTemplate, ISlopeData> {
       const slopes = this.app.queryStore
         .queryByType<Slope>(Slope.Type)
         .filter((g) => {
-          const refSlopeKiloMarker = this.app.queryStore.queryById(
-            g.datas.refDeviceId[0]
-          ) as SlopeKiloMarker;
+          let refSlopeKiloMarker;
+          try {
+            refSlopeKiloMarker = this.app.queryStore.queryById(
+              g.datas.refDeviceId[0]
+            ) as SlopeKiloMarker;
+          } catch (error) {
+            this.app.deleteGraphics(g);
+          }
+
           return (
-            refSlopeKiloMarker.datas.kilometerSystem[0].direction == dirSlop
+            refSlopeKiloMarker?.datas.kilometerSystem[0].direction == dirSlop
           );
         });
       const slopeKiloMarkers = this.app.queryStore