diff --git a/backends/com_backend.py b/backends/com_backend.py
index 7436dec..5f506d7 100644
--- a/backends/com_backend.py
+++ b/backends/com_backend.py
@@ -3990,15 +3990,18 @@ class ComBackend(AutoCADBackend):
         return await self._run(_sync)
 
     async def system_get_variable(self, name) -> Any:
+        # GetVariable / SetVariable are members of AcadDocument, not of
+        # AcadApplication: `AutoCAD.Application.GetVariable` raises
+        # AttributeError on a live seat before anything reaches AutoCAD.
         def _sync():
-            app = _acad_app()
-            return app.GetVariable(name)
+            doc = _acad_doc()
+            return doc.GetVariable(name)
 
         return await self._run(_sync)
 
     async def system_set_variable(self, name, value) -> dict:
         def _sync():
-            app = _acad_app()
+            doc = _acad_doc()  # the sysvar host is the document (see system_get_variable)
             # Coerce to the sysvar's actual type (NEW-com-set-variable-coercion):
             # AutoCAD rejects e.g. a string "0" for the integer OSMODE. Probe the
             # current value's type and convert to match; pass through on failure.
@@ -4010,7 +4013,7 @@ class ComBackend(AutoCADBackend):
             # AutoCAD had already applied the write.
             payload = value
             try:
-                current = app.GetVariable(name)
+                current = doc.GetVariable(name)
                 if isinstance(current, bool):
                     coerced = bool(int(value)) if isinstance(value, str) else bool(value)
                 elif isinstance(current, int):
@@ -4027,7 +4030,7 @@ class ComBackend(AutoCADBackend):
                 payload = _av(coerced) if isinstance(current, (tuple, list)) else coerced
             except Exception as exc:
                 log.debug("set_variable type probe for %s failed: %s", name, exc)
-            app.SetVariable(name, payload)
+            doc.SetVariable(name, payload)
             return {"ok": True, "variable": name, "value": coerced}
 
         return await self._run(_sync)
diff --git a/tests/test_com_backend.py b/tests/test_com_backend.py
index 8646a5f..3033553 100644
--- a/tests/test_com_backend.py
+++ b/tests/test_com_backend.py
@@ -317,6 +317,19 @@ async def test_com_backend_connects():
 # number it already has?
 
 
+@pytest.fixture(autouse=True)
+def _restore_acad_doc():
+    """`_measure_backend` swaps the module-level `_acad_doc`; put it back after
+    every test here. Left in place, the MagicMock document leaked into every
+    later test of the session that resolves the document itself (the settings
+    facade's COM tests read sysvars through `_acad_doc()`)."""
+    import backends.com_backend as cb
+
+    original = cb._acad_doc
+    yield
+    cb._acad_doc = original
+
+
 def _measure_backend(entity):
     """A ComBackend whose HandleToObject returns exactly this entity."""
     import backends.com_backend as cb
@@ -329,7 +342,7 @@ def _measure_backend(entity):
     backend._run = _run
     doc = MagicMock()
     doc.HandleToObject.return_value = entity
-    cb._acad_doc = lambda: doc
+    cb._acad_doc = lambda: doc  # restored by `_restore_acad_doc`
     return backend
 
 
diff --git a/tests/test_com_sprint3.py b/tests/test_com_sprint3.py
index 743ff11..b90c35f 100644
--- a/tests/test_com_sprint3.py
+++ b/tests/test_com_sprint3.py
@@ -55,14 +55,16 @@ class _Doc:
 
 
 async def test_set_variable_coerces_string_to_sysvar_int_type(monkeypatch):
-    app = MagicMock()
-    app.GetVariable.return_value = 4159  # OSMODE current value is an int
-    monkeypatch.setattr(cb, "_acad_app", lambda: app)
+    # GetVariable / SetVariable are AcadDocument members (the Application has
+    # neither), so the fake is the document that `_acad_doc()` returns.
+    doc = MagicMock()
+    doc.GetVariable.return_value = 4159  # OSMODE current value is an int
+    monkeypatch.setattr(cb, "_acad_doc", lambda: doc)
 
     b = _backend_no_executor()
     out = await b.system_set_variable("OSMODE", "0")
 
-    name, val = app.SetVariable.call_args[0]
+    name, val = doc.SetVariable.call_args[0]
     assert name == "OSMODE"
     assert val == 0 and isinstance(val, int)  # coerced from "0" to int 0
     assert out["value"] == 0