diff --git a/tools/extract/tests/test_overview.py b/tools/extract/tests/test_overview.py
index 8b41e05..8ce882b 100644
--- a/tools/extract/tests/test_overview.py
+++ b/tools/extract/tests/test_overview.py
@@ -83,3 +83,29 @@ def test_debug_overview_still_draws_palms(tmp_path):
     stats = overview.render(src, dst)
     assert stats["palmen"] == 1
     assert Image.open(dst).getpixel((100, 100)) == overview.PALM   # 200 m bei 0,5 px/m
+
+
+def test_walkable_mask_marks_roads_bridges_and_surfaces_without_land(tmp_path):
+    """Jede begehbare Ebene für sich, ohne Land darunter: sonst verdeckt das Land einen Fehler."""
+    src = tmp_path / "chunks"
+    src.mkdir()
+    chunk = {
+        "chunk": [0, 0],
+        "origin": [SLICE["x0"], -SLICE["y1"]],
+        "land": [],
+        "surfaces": [{"poly": [_ring(0, 0, 40, 40)], "kind": "sand"}],
+        "roads": [{"poly": [_ring(100, 0, 120, 40)], "bridge": False},
+                  {"poly": [_ring(200, 0, 220, 40)], "bridge": True}],
+        "centerlines": [],
+        "buildings": [],
+        "palms": [],
+    }
+    (src / "chunk_0_0.json").write_text(json.dumps(chunk))
+    (src / "manifest.json").write_text('{"slice": "vice-a"}\n')
+    dst = tmp_path / "out"
+    overview.render_map(src, dst)
+    mask = Image.open(dst / "map-walkable.png")
+    assert mask.getpixel((5, 5)) == overview.WALKABLE      # Sand bei 20 m / 20 m
+    assert mask.getpixel((27, 5)) == overview.WALKABLE     # Straße bei 110 m / 20 m
+    assert mask.getpixel((52, 5)) == overview.WALKABLE     # Brücke bei 210 m / 20 m
+    assert mask.getpixel((40, 5)) == overview.BLOCKED      # Wasser bei 160 m / 20 m