diff --git a/fastkml/geometry.py b/fastkml/geometry.py
index 343df712..6b314140 100644
--- a/fastkml/geometry.py
+++ b/fastkml/geometry.py
@@ -1035,7 +1035,7 @@ class Polygon(_Geometry):
     """
 
     outer_boundary: Optional[OuterBoundaryIs]
-    inner_boundaries: Optional[List[InnerBoundaryIs]]
+    inner_boundaries: List[InnerBoundaryIs]
 
     def __init__(
         self,
diff --git a/tests/geometries/boundaries_test.py b/tests/geometries/boundaries_test.py
index 181bb066..4b413f08 100644
--- a/tests/geometries/boundaries_test.py
+++ b/tests/geometries/boundaries_test.py
@@ -59,19 +59,13 @@ def test_read_outer_boundary(self) -> None:
     def test_inner_boundary(self) -> None:
         """Test the init method."""
         coords = ((1, 2), (2, 0), (0, 0), (1, 2))
+
         inner_boundary = InnerBoundaryIs(
             kml_geometry=LinearRing(kml_coordinates=Coordinates(coords=coords)),
         )
 
-def test_inner_boundary(self) -> None:
-    """Test the init method and __bool__."""
-    coords = ((1, 2), (2, 0), (0, 0), (1, 2))
-    inner_boundary = InnerBoundaryIs(
-        kml_geometry=LinearRing(kml_coordinates=Coordinates(coords=coords)),
-    )
-
-    assert inner_boundary.geometry == geo.LinearRing(coords)
-    assert bool(inner_boundary) is True
+        assert inner_boundary.geometry == geo.LinearRing(coords)
+        assert bool(inner_boundary)
         assert inner_boundary.to_string(prettyprint=False).strip() == (
             '<kml:innerBoundaryIs xmlns:kml="http://www.opengis.net/kml/2.2">'
             "<kml:LinearRing><kml:coordinates>"
diff --git a/tests/geometries/polygon_test.py b/tests/geometries/polygon_test.py
index 7cb8dae2..13763494 100644
--- a/tests/geometries/polygon_test.py
+++ b/tests/geometries/polygon_test.py
@@ -18,6 +18,7 @@
 
 import pygeoif.geometry as geo
 
+from fastkml.geometry import OuterBoundaryIs
 from fastkml.geometry import Polygon
 from tests.base import Lxml
 from tests.base import StdLibrary
@@ -180,7 +181,7 @@ def test_empty_polygon(self) -> None:
 
         assert not polygon.geometry
         assert polygon.outer_boundary is not None
-        assert isinstance(polygon.outer_boundary, LinearRing)
+        assert isinstance(polygon.outer_boundary, OuterBoundaryIs)
         assert len(polygon.inner_boundaries) == 0
         assert "tessellate>1</" in polygon.to_string()