diff --git a/plotpy/items/shape/polygon.py b/plotpy/items/shape/polygon.py
index 207c278..a739a91 100644
--- a/plotpy/items/shape/polygon.py
+++ b/plotpy/items/shape/polygon.py
@@ -276,8 +276,10 @@ def draw(
         painter.setBrush(brush)
         points = self.transform_points(xMap, yMap)
         if self.ADDITIONNAL_POINTS:
-            shape_points = points[: -self.ADDITIONNAL_POINTS]
-            other_points = points[-self.ADDITIONNAL_POINTS :]
+            # Slice indexing is not supported by PySide6, so we convert the `QPolygonF`
+            # object to a list before converting it back to a `QPolygonF` object:
+            shape_points = QG.QPolygonF(list(points[: -self.ADDITIONNAL_POINTS]))
+            other_points = QG.QPolygonF(list(points[-self.ADDITIONNAL_POINTS :]))
         else:
             shape_points = points
             other_points = []