diff --git a/CHANGELOG.md b/CHANGELOG.md
index 29b90f26a54..4b2afb55bca 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -204,6 +204,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Fixed bug in `compas.datastructures.Mesh.insert_vertex`.
 * Fixed bug in `compas.geometry.angle_vectors_signed`.
 * Changed `compas.artists.MeshArtist` default colors.
+* Fixed bug in `compas.geometry.curves.Polyline` shorten and extend methods.
 
 ### Removed
 
diff --git a/src/compas/geometry/curves/polyline.py b/src/compas/geometry/curves/polyline.py
index dee9f9a19d2..9daf1e8e59d 100644
--- a/src/compas/geometry/curves/polyline.py
+++ b/src/compas/geometry/curves/polyline.py
@@ -578,10 +578,10 @@ def extend(self, length):
         """
         try:
             start, end = length
-            self.points[0] = self.points[0] + self.lines[0].vector.unitized().scaled(-start)
+            self[0] = self[0] + self.lines[0].vector.unitized().scaled(-start)
         except TypeError:
             start = end = length
-        self.points[-1] = self.points[-1] + self.lines[-1].vector.unitized().scaled(end)
+        self[-1] = self[-1] + self.lines[-1].vector.unitized().scaled(end)
 
     def extended(self, length):
         """Returns a copy of this polyline extended by a given length.
@@ -643,6 +643,7 @@ def shorten(self, length):
             else:
                 self.points[-1] = line.start + line.vector.unitized().scaled(total_length - end)
                 break
+        self._lines = None
 
     def shortened(self, length):
         """Returns a copy of this polyline shortened by a given length.
diff --git a/tests/compas/geometry/test_curves_polyline.py b/tests/compas/geometry/test_curves_polyline.py
index 8747759e31e..086d34a2fed 100644
--- a/tests/compas/geometry/test_curves_polyline.py
+++ b/tests/compas/geometry/test_curves_polyline.py
@@ -432,54 +432,28 @@ def test_polyline_tangent_at_point(coords, input, expected):
 
 
 @pytest.mark.parametrize(
-    "coords,input,expected",
+    "coords,input,expected,length",
     [
-        (
-            [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]],
-            1.5,
-            [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 3.5, 0]],
-        ),
-        (
-            [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]],
-            -2.5,
-            [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, -0.5, 0]],
-        ),
-        (
-            [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]],
-            (2, 2),
-            [[-2, 0, 0], [1, 0, 0], [2, 0, 0], [2, 4, 0]],
-        ),
-        (
-            [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]],
-            (2, 0),
-            [[-2, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]],
-        ),
+        ([[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]], 1.5, [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 3.5, 0]], 5.5),
+        ([[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]], -2.5, [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, -0.5, 0]], 2.5),
+        ([[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]], (2, 2), [[-2, 0, 0], [1, 0, 0], [2, 0, 0], [2, 4, 0]], 8),
+        ([[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]], (2, 0), [[-2, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]], 6),
     ],
 )
-def test_polyline_extend(coords, input, expected):
-    assert expected == Polyline(coords).extended(input)
+def test_polyline_extend(coords, input, expected, length):
+    polyline = Polyline(coords).extended(input)
+    assert expected == polyline and length == polyline.length
 
 
 @pytest.mark.parametrize(
-    "coords,input,expected",
+    "coords,input,expected,length",
     [
-        (
-            [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]],
-            0.5,
-            [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 1.5, 0]],
-        ),
-        (
-            [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]],
-            2,
-            [[0, 0, 0], [1, 0, 0], [2, 0, 0]],
-        ),
-        (
-            [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]],
-            (0.5, 2.5),
-            [[0.5, 0, 0], [1, 0, 0], [1.5, 0, 0]],
-        ),
-        ([[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]], (1, 2), [[1, 0, 0], [2, 0, 0]]),
+        ([[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]], 0.5, [[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 1.5, 0]], 3.5),
+        ([[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]], 2, [[0, 0, 0], [1, 0, 0], [2, 0, 0]], 2),
+        ([[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]], (0.5, 2.5), [[0.5, 0, 0], [1, 0, 0], [1.5, 0, 0]], 1),
+        ([[0, 0, 0], [1, 0, 0], [2, 0, 0], [2, 2, 0]], (1, 2), [[1, 0, 0], [2, 0, 0]], 1),
     ],
 )
-def test_polyline_shortened(coords, input, expected):
-    assert expected == Polyline(coords).shortened(input)
+def test_polyline_shortened(coords, input, expected, length):
+    polyline = Polyline(coords).shortened(input)
+    assert expected == polyline and length == polyline.length