diff --git a/src/core/abut/wings.ts b/src/core/abut/wings.ts
index fd1da01..1c72592 100644
--- a/src/core/abut/wings.ts
+++ b/src/core/abut/wings.ts
@@ -120,8 +120,9 @@ export function buildWings(model: AbutModel, members: AbutMembers, forms?: { lef
     const backTopAt = (s: number) => members.parapetTopStartEl + ((members.parapetTopEndEl - members.parapetTopStartEl) * s) / model.length - members.shape.bracketHeightM;
     const haunchAt = (kind: 'upper' | 'lower', t: number): Haunch => {
       const d = Math.abs(t) / k;
-      const c = pointAt(d);
+      // The corner lies on the 날개벽 내측면 (the face between the two wings), WING_THICKNESS_M in from the axis end.
       const inwardUnit = { e: model.u.e * a, n: model.u.n * a };
+      const c = shift(pointAt(d), inwardUnit, WING_THICKNESS_M);
       const corners: [AbutPoint, AbutPoint, AbutPoint] = [c, shift(c, w, HAUNCH_LEG_M), shift(c, inwardUnit, HAUNCH_LEG_M)];
       return {
         kind,
diff --git a/tests/abut-blocks-slab.test.ts b/tests/abut-blocks-slab.test.ts
index d6a337c..73f8de7 100644
--- a/tests/abut-blocks-slab.test.ts
+++ b/tests/abut-blocks-slab.test.ts
@@ -101,4 +101,29 @@ describe('교대 3D: 받침블럭과 접속슬래브 (spec §4.2, §4.8)', () =>
       if (pos.getZ(i) >= members.shape.wallBackM) expect(pos.getY(i)).toBeGreaterThanOrEqual(backTop(pos.getX(i)) - 1e-6);
     }
   });
+
+  it('the 헌치 sits on the 날개벽 내측면 (the face between the two wings), on the centre side, and does not enter the wing', () => {
+    const axis = (p: { e: number; n: number }) => {
+      const d = { e: p.e - model.ip1.e, n: p.n - model.ip1.n };
+      const f = { e: model.nLeft.e * model.frontSide, n: model.nLeft.n * model.frontSide };
+      return { s: d.e * model.u.e + d.n * model.u.n, t: d.e * f.e + d.n * f.n };
+    };
+    // Inner face of each wing: s = sEnd + a·0.45 + (ws/wt)·t (a = +1 at IP1, −1 at IP3). Haunch vertices must lie on the centre side of it.
+    const inner = wings.map((w) => {
+      const p0 = axis(w.corners[0]);
+      const p1 = axis(w.corners[1]);
+      const a = w.sEnd === 0 ? 1 : -1;
+      return { sEnd: w.sEnd, a, k: (p1.s - p0.s) / (p1.t - p0.t), tRoot: p0.t };
+    });
+    for (const h of (named('haunches') as THREE.Group).children) {
+      const pos = (h as THREE.Mesh).geometry.getAttribute('position');
+      for (let i = 0; i < pos.count; i++) {
+        const x = pos.getX(i);
+        const z = pos.getZ(i);
+        const w = x < model.length / 2 ? inner[0] : inner[1];
+        const sIn = w.sEnd + w.a * 0.45 + w.k * (z - w.tRoot);
+        expect(w.a * (x - sIn)).toBeGreaterThanOrEqual(-1e-6);
+      }
+    }
+  });
 });