diff --git a/B05_Profile/B05_Profile_UI_Markers.ts b/B05_Profile/B05_Profile_UI_Markers.ts
index e7b95c19..0ceb8bf7 100644
--- a/B05_Profile/B05_Profile_UI_Markers.ts
+++ b/B05_Profile/B05_Profile_UI_Markers.ts
@@ -8,7 +8,8 @@ export interface PlacedRoutePoint {
   type: RoutePointKind;
   x: number;
   y: number;
-  z: number;
+  /** 표고(m). `null`은 **모른다**는 뜻 — 계획노선 CSV로 만든 점이 그렇다. 0으로 눕히면 안 된다. */
+  z: number | null;
   radius_m?: number;
 }
 
@@ -72,7 +73,7 @@ function disposeGroup(group: THREE.Group): void {
   group.clear();
 }
 
-export function modelToScene(point: Pick<PlacedRoutePoint, "x" | "y" | "z">, bounds: ModelBounds) {
+export function modelToScene(point: { x: number; y: number; z: number }, bounds: ModelBounds) {
   const cx = (bounds.x[0] + bounds.x[1]) / 2;
   const cy = (bounds.y[0] + bounds.y[1]) / 2;
   const cz = (bounds.z[0] + bounds.z[1]) / 2;
diff --git a/B05_Profile/B05_Profile_UI_Page.ts b/B05_Profile/B05_Profile_UI_Page.ts
index f5f1eeb2..2ca77a05 100644
--- a/B05_Profile/B05_Profile_UI_Page.ts
+++ b/B05_Profile/B05_Profile_UI_Page.ts
@@ -97,7 +97,8 @@ function placed(
     type,
     x: point.x,
     y: point.y,
-    z: point.z ?? 0,
+    // 표고를 모르면 모르는 채로 넘긴다 — 0으로 눕히면 마커가 지형 한참 아래 평면에 깔린다.
+    z: point.z ?? null,
     ...(type === "ap" || type === "fp" ? { radius_m: (point as CirclePoint).radius_m ?? 25 } : {}),
   };
 }
@@ -114,7 +115,8 @@ function restorePoints(latest: RouteLatestResponse): RouteDesignPoints {
 }
 
 function routePoint(point: PlacedRoutePoint): RoutePoint {
-  return { x: point.x, y: point.y, z: point.z };
+  // 서버 스키마는 표고를 빼면 "모름"으로 받는다 — null은 undefined로 바꿔 보낸다.
+  return { x: point.x, y: point.y, z: point.z ?? undefined };
 }
 
 function circlePoint(point: PlacedRoutePoint): CirclePoint {