diff --git a/netboxlabs/diode/sdk/ingester.py b/netboxlabs/diode/sdk/ingester.py
index c37d7c0..b742707 100644
--- a/netboxlabs/diode/sdk/ingester.py
+++ b/netboxlabs/diode/sdk/ingester.py
@@ -7007,7 +7007,10 @@ def __new__(
         if site is not None:
             if device is not None and not device.HasField("site"):
                 device.site.CopyFrom(site)
-            if cluster is not None and not cluster.HasField("scope_site"):
+            # scope_site shares a oneof with scope_location/region/site_group, so
+            # HasField("scope_site") is False while a sibling holds the scope and
+            # CopyFrom would silently clear it.
+            if cluster is not None and not cluster.WhichOneof("scope"):
                 cluster.scope_site.CopyFrom(site)
         if role is not None:
             if device is not None and not device.HasField("role"):
diff --git a/tests/test_ingester.py b/tests/test_ingester.py
index 1c9b5b8..853a62a 100644
--- a/tests/test_ingester.py
+++ b/tests/test_ingester.py
@@ -43,6 +43,7 @@
     Prefix,
     Role,
     Site,
+    SiteGroup,
     Tag,
     VirtualDisk,
     VMInterface,
@@ -608,6 +609,22 @@ def test_virtual_machine_instantiation_with_cluster_without_site():
     assert virtual_machine.cluster.scope_site.name == "Site1"
 
 
+def test_virtual_machine_instantiation_keeps_cluster_scope_site_group():
+    """Check VirtualMachine leaves a cluster that is already scoped to a SiteGroup untouched."""
+    cluster = Cluster(name="gc-us-east1", scope_site_group=SiteGroup(name="SiteGroup1"))
+
+    virtual_machine = VirtualMachine(
+        name="vm1",
+        cluster=cluster,
+        site=Site(name="Site1"),
+    )
+
+    assert cluster.WhichOneof("scope") == "scope_site_group"
+    assert cluster.scope_site_group.name == "SiteGroup1"
+    assert virtual_machine.cluster.WhichOneof("scope") == "scope_site_group"
+    assert virtual_machine.cluster.scope_site_group.name == "SiteGroup1"
+
+
 def test_virtual_disk_instantiation_with_all_fields():
     """Check VirtualDisk instantiation with all fields."""
     virtual_disk = VirtualDisk(