diff --git a/src/presa_mano/api/grasp_routes.py b/src/presa_mano/api/grasp_routes.py
index 4156575..38331b2 100644
--- a/src/presa_mano/api/grasp_routes.py
+++ b/src/presa_mano/api/grasp_routes.py
@@ -149,8 +149,7 @@ def _points_via_sam21(nuwa, bbox: tuple[int, int, int, int], sw: Stopwatch) -> n
     except (NuwaError, httpx.RequestError) as e:
         raise HTTPException(status_code=502, detail=f"Nuwa unreachable: {e}")
 
-    rgb_intr = intr_full.get("rgb")
-    if not rgb_intr:
+    if not intr_full.get("rgb"):
         log.warning("SAM21 path skipped: nuwa intrinsics missing 'rgb' block")
         raise _Sam21Fallback("nuwa intrinsics missing 'rgb' block")
 
@@ -162,6 +161,7 @@ def _points_via_sam21(nuwa, bbox: tuple[int, int, int, int], sw: Stopwatch) -> n
         if bgr is None:
             log.warning("SAM21 path skipped: could not decode Nuwa RGB JPEG")
             raise _Sam21Fallback("could not decode Nuwa RGB JPEG")
+        h_rgb, w_rgb = bgr.shape[:2]
         ok, rgb_png_buf = cv2.imencode(".png", bgr)
         if not ok:
             log.warning("SAM21 path skipped: could not re-encode RGB as PNG")
@@ -178,6 +178,15 @@ def _points_via_sam21(nuwa, bbox: tuple[int, int, int, int], sw: Stopwatch) -> n
                 log.warning("SAM21 path skipped: depth PNG dtype %s (expected uint16)",
                             depth_ir.dtype)
                 raise _Sam21Fallback(f"depth PNG dtype expected uint16, got {depth_ir.dtype}")
+            h_ir, w_ir = depth_ir.shape
+            # Nuwa /api/intrinsics omits width/height — inject the real ones
+            # from the decoded images so CameraRegistration and SAM21 agree on
+            # frame sizes.
+            intr_full = {
+                **intr_full,
+                "rgb": {**intr_full["rgb"], "width": w_rgb, "height": h_rgb},
+                "ir": {**intr_full.get("ir", {}), "width": w_ir, "height": h_ir},
+            }
             reg = CameraRegistration.from_nuwa(intr_full)
             depth_aligned = align_depth_to_rgb(depth_ir, reg)
             ok, depth_png_buf = cv2.imencode(".png", depth_aligned)
@@ -196,7 +205,7 @@ def _points_via_sam21(nuwa, bbox: tuple[int, int, int, int], sw: Stopwatch) -> n
             pts_cv = _deps.sam21().segment_pointcloud(
                 rgb_png=rgb_png,
                 depth_png=depth_png_out,
-                intrinsics=rgb_intr,
+                intrinsics=intr_full["rgb"],
                 bbox=bbox,
                 depth_scale_mm=1.0,
             )