diff --git a/source/blender/makesrna/intern/rna_scene.cc b/source/blender/makesrna/intern/rna_scene.cc
index b47912f5ddb..b21a9864836 100644
--- a/source/blender/makesrna/intern/rna_scene.cc
+++ b/source/blender/makesrna/intern/rna_scene.cc
@@ -1258,7 +1258,11 @@ static void rna_Scene_compositing_node_group_set(PointerRNA *ptr,
         reports, RPT_ERROR, "Node tree '%s' is not a compositing node group.", ntree->id.name + 2);
     return;
   }
+  if (scene->compositing_node_group) {
+    id_us_min(&scene->compositing_node_group->id);
+  }
   scene->compositing_node_group = ntree;
+  id_us_plus(&scene->compositing_node_group->id);
 }
 
 static std::optional<std::string> rna_SceneEEVEE_path(const PointerRNA * /*ptr*/)
diff --git a/tests/python/CMakeLists.txt b/tests/python/CMakeLists.txt
index 500c247f822..551d73b5afa 100644
--- a/tests/python/CMakeLists.txt
+++ b/tests/python/CMakeLists.txt
@@ -1035,6 +1035,11 @@ if(WITH_GPU_COMPOSITOR_TESTS AND TEST_SRC_DIR_EXISTS)
   endif()
 endif()
 
+add_blender_test(
+  compositing_node_group
+  --python ${CMAKE_CURRENT_LIST_DIR}/compositing_node_group.py
+)
+
 # ------------------------------------------------------------------------------
 # GEOMETRY NODE TESTS
 # ------------------------------------------------------------------------------
diff --git a/tests/python/compositing_node_group.py b/tests/python/compositing_node_group.py
new file mode 100644
index 00000000000..79a529cfbb6
--- /dev/null
+++ b/tests/python/compositing_node_group.py
@@ -0,0 +1,26 @@
+# SPDX-FileCopyrightText: 2025 Blender Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+import bpy
+import unittest
+
+
+class CompositingNodeGroupTest(unittest.TestCase):
+    """
+    Tests specific to the root compositing node tree
+    """
+
+    def setUp(self):
+        bpy.ops.wm.read_factory_settings(use_empty=True)
+
+    def test_assign_invalid(self):
+        scene = bpy.data.scenes["Scene"]
+        with self.assertRaises(RuntimeError):
+            scene.compositing_node_group = bpy.data.node_groups.new("invalid", "GeometryNodeTree")
+
+
+if __name__ == "__main__":
+    import sys
+    sys.argv = [__file__] + (sys.argv[sys.argv.index("--") + 1:] if "--" in sys.argv else [])
+    unittest.main()