diff --git a/CHANGELOG.md b/CHANGELOG.md
index adbfeb3..914fc7c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,10 @@ _Next: closed-loop refiner (critique→repair→re-critique with transaction-sta
   matching the project name, so hatchling could not infer which files to ship.
   `pyproject.toml` now declares the wheel file selection explicitly
   (`server.py`, `config.py`, `security.py`, `backends/`, `engineering/`). (#2)
+- **`dimension_linear` on the COM backend** — always crashed with
+  `<unknown>.AddDimLinear`: the AutoCAD ActiveX API has no `AddDimLinear`
+  method. Linear dimensions are now created via `AddDimRotated` (identical
+  argument order), with a mocked regression test. (#3)
 
 ## [1.2.0] — 2026-07-07
 
diff --git a/backends/com_backend.py b/backends/com_backend.py
index 21eecbc..3a1e2f3 100644
--- a/backends/com_backend.py
+++ b/backends/com_backend.py
@@ -824,7 +824,9 @@ class ComBackend(AutoCADBackend):
     ) -> EntityInfo:
         def _sync():
             mspace = _msp()
-            dim = mspace.AddDimLinear(
+            # The ActiveX API has no AddDimLinear — rotated linear dims are
+            # created with AddDimRotated (GH issue #3).
+            dim = mspace.AddDimRotated(
                 _apoint(x1, y1), _apoint(x2, y2),
                 _apoint(dim_x, dim_y), deg2rad(rotation),
             )
diff --git a/tests/test_com_backend.py b/tests/test_com_backend.py
index 916bbc9..73d1829 100644
--- a/tests/test_com_backend.py
+++ b/tests/test_com_backend.py
@@ -211,6 +211,42 @@ def test_safe_send_command_new_handle_detection():
     assert set(result) == {"1C", "1D"}
 
 
+# ---------------------------------------------------------------------------
+# dimension_linear — must use AddDimRotated (GH issue #3)
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_dimension_linear_uses_add_dim_rotated():
+    """Regression for GH issue #3: the AutoCAD ActiveX API has no AddDimLinear
+    method — calling it raised ``<unknown>.AddDimLinear``. Linear dimensions
+    must go through AddDimRotated."""
+    backend = ComBackend()
+
+    async def _run_inline(func, *args, **kwargs):
+        return func(*args, **kwargs)
+
+    backend._run = _run_inline  # bypass the COM executor thread
+
+    mspace = MagicMock()
+    with (
+        patch("backends.com_backend._msp", return_value=mspace),
+        patch("backends.com_backend._apoint", side_effect=lambda *a: tuple(float(v) for v in a)),
+        patch("backends.com_backend._regen"),
+        patch("backends.com_backend._apply_dim_tolerance"),
+        patch("backends.com_backend._entity_info", side_effect=lambda e: e),
+    ):
+        await backend.dimension_linear(0, 0, 100, 0, 50, 20, rotation=0.0)
+
+    mspace.AddDimRotated.assert_called_once()
+    mspace.AddDimLinear.assert_not_called()
+    args = mspace.AddDimRotated.call_args[0]
+    assert args[0] == (0.0, 0.0)      # ext line 1 origin
+    assert args[1] == (100.0, 0.0)    # ext line 2 origin
+    assert args[2] == (50.0, 20.0)    # dim line location
+    assert args[3] == pytest.approx(0.0)  # rotation in radians
+
+
 # ---------------------------------------------------------------------------
 # Live integration — skipped unless AutoCAD is reachable
 # ---------------------------------------------------------------------------