diff --git a/models/issue-400-num-face-vertices.obj b/models/issue-400-num-face-vertices.obj
new file mode 100644
index 00000000..77e25b48
--- /dev/null
+++ b/models/issue-400-num-face-vertices.obj
@@ -0,0 +1,15 @@
+# Regression test model for issue #400 - numpy_num_face_vertices()
+# Mixed quad and triangle faces to verify correct uint type handling.
+# With the bug (unsigned char instead of unsigned int in the numpy binding),
+# numpy_num_face_vertices() returned all zeros for quad (4-vertex) faces.
+v 0.0 0.0 0.0
+v 1.0 0.0 0.0
+v 1.0 1.0 0.0
+v 0.0 1.0 0.0
+v 0.5 0.5 1.0
+# quad face (num_face_vertices = 4)
+f 1 2 3 4
+# triangle face (num_face_vertices = 3)
+f 1 2 5
+# triangle face (num_face_vertices = 3)
+f 2 3 5
diff --git a/tests/python/tinyobjloader_tests/test_loader.py b/tests/python/tinyobjloader_tests/test_loader.py
index 8d7b8f50..c9159ea1 100644
--- a/tests/python/tinyobjloader_tests/test_loader.py
+++ b/tests/python/tinyobjloader_tests/test_loader.py
@@ -1,7 +1,11 @@
+from pathlib import Path
+
 import numpy as np
 
 from .loader import Loader, LoadException
 
+MODELS_DIR = Path(__file__).parent.parent.parent.parent / "models"
+
 TWO_QUADS = """
 v 0 0 0
 v 0 0 0
@@ -130,7 +134,32 @@ def test_numpy_index_array_two_quads():
     assert [x.vertex_index for x in shape.mesh.indices] == expected_vertex_index
 
     # Test.
-    expected_numpy_indices = [0, -1, -1, 1, -1, -1, 2, -1, -1, 3, -1, -1, 4, -1, -1, 5, -1, -1, 6, -1, -1, 7, -1, -1]
+    expected_numpy_indices = [
+        0,
+        -1,
+        -1,
+        1,
+        -1,
+        -1,
+        2,
+        -1,
+        -1,
+        3,
+        -1,
+        -1,
+        4,
+        -1,
+        -1,
+        5,
+        -1,
+        -1,
+        6,
+        -1,
+        -1,
+        7,
+        -1,
+        -1,
+    ]
     np.testing.assert_array_equal(shape.mesh.numpy_indices(), expected_numpy_indices)
 
 
@@ -174,3 +203,33 @@ def test_numpy_vertex_array_two_quads():
 
     # Test.
     np.testing.assert_array_almost_equal(loader.attrib.numpy_vertices(), expected_vertices, decimal=6)
+
+
+def test_numpy_num_face_vertices_from_file():
+    """
+    Regression test for https://github.com/tinyobjloader/tinyobjloader/issues/400
+
+    Loads a mixed quad/triangle mesh from a .obj file and checks that
+    numpy_num_face_vertices() returns correct unsigned int values.
+    With the bug (unsigned char element type), values were read as zeros.
+    """
+
+    # Set up.
+    obj_path = str(MODELS_DIR / "issue-400-num-face-vertices.obj")
+    loader = Loader(triangulate=False)
+    loader.load(obj_path)
+
+    shapes = loader.shapes
+    assert len(shapes) == 1
+
+    (shape,) = shapes
+    # The file has one quad face (4 vertices) and two triangle faces (3 vertices each).
+    expected_num_face_vertices = [4, 3, 3]
+
+    # Confidence check using the non-numpy accessor.
+    assert shape.mesh.num_face_vertices == expected_num_face_vertices
+
+    # Test: numpy_num_face_vertices() must return the same values with the correct dtype.
+    result = shape.mesh.numpy_num_face_vertices()
+    np.testing.assert_array_equal(result, expected_num_face_vertices)
+    assert result.dtype == np.dtype("uint32")