diff --git a/labelme_toolkit/_cli/_ai_annotate_rectangles.py b/labelme_toolkit/_cli/_ai_annotate_rectangles.py
index 5e8bdfc..82cbf3a 100644
--- a/labelme_toolkit/_cli/_ai_annotate_rectangles.py
+++ b/labelme_toolkit/_cli/_ai_annotate_rectangles.py
@@ -42,10 +42,13 @@ def _ai_annotate_rectangles(
     for annotation in response.annotations:
         shape: _labelme.Shape = _labelme.Shape(
             type="rectangle",
-            points=[
-                [annotation.bounding_box.xmin, annotation.bounding_box.ymin],
-                [annotation.bounding_box.xmax, annotation.bounding_box.ymax],
-            ],
+            points=np.array(
+                [
+                    [annotation.bounding_box.xmin, annotation.bounding_box.ymin],
+                    [annotation.bounding_box.xmax, annotation.bounding_box.ymax],
+                ],
+                dtype=np.float32,
+            ),
             label=annotation.text,
         )
         shape_dict: Dict = shape.to_json()
diff --git a/labelme_toolkit/_labelme.py b/labelme_toolkit/_labelme.py
index 8f4c8c5..f0bb45a 100644
--- a/labelme_toolkit/_labelme.py
+++ b/labelme_toolkit/_labelme.py
@@ -110,6 +110,7 @@ def draw_shape_(
     elif shape.type == "polygon":
         draw.polygon(xy=points, fill=fill_color, outline=line_color, width=line_width)
     elif shape.type == "mask":
+        assert shape.mask is not None
         mask_height, mask_width = shape.mask.shape
         (xmin, ymin), (xmax, ymax) = points
         mask = PIL.Image.fromarray(shape.mask)