diff --git a/panda/src/pgraph/lightAttrib.cxx b/panda/src/pgraph/lightAttrib.cxx
index 15b010336e..40014c53ee 100644
--- a/panda/src/pgraph/lightAttrib.cxx
+++ b/panda/src/pgraph/lightAttrib.cxx
@@ -841,6 +841,9 @@ compose_impl(const RenderAttrib *other) const {
     lobj->attrib_ref();
   }
 
+  // This is needed since _sorted_on_lights is not yet populated.
+  new_attrib->_sort_seq = UpdateSeq::old();
+
   return return_new(new_attrib);
 }
 
diff --git a/tests/pgraph/test_lightattrib.py b/tests/pgraph/test_lightattrib.py
new file mode 100644
index 0000000000..752f4c2717
--- /dev/null
+++ b/tests/pgraph/test_lightattrib.py
@@ -0,0 +1,74 @@
+from panda3d import core
+
+# Some dummy lights we can use for our light attributes.
+spot = core.NodePath(core.Spotlight("spot"))
+point = core.NodePath(core.PointLight("point"))
+ambient = core.NodePath(core.AmbientLight("ambient"))
+
+
+def test_lightattrib_compose_add():
+    # Tests a case in which a child node adds another light.
+    lattr1 = core.LightAttrib.make()
+    lattr1 = lattr1.add_on_light(spot)
+
+    lattr2 = core.LightAttrib.make()
+    lattr2 = lattr2.add_on_light(point)
+
+    lattr3 = lattr1.compose(lattr2)
+    assert lattr3.get_num_on_lights() == 2
+
+    assert spot in lattr3.on_lights
+    assert point in lattr3.on_lights
+
+
+def test_lightattrib_compose_subtract():
+    # Tests a case in which a child node disables a light.
+    lattr1 = core.LightAttrib.make()
+    lattr1 = lattr1.add_on_light(spot)
+    lattr1 = lattr1.add_on_light(point)
+
+    lattr2 = core.LightAttrib.make()
+    lattr2 = lattr2.add_off_light(ambient)
+    lattr2 = lattr2.add_off_light(point)
+
+    lattr3 = lattr1.compose(lattr2)
+    assert lattr3.get_num_on_lights() == 1
+
+    assert spot in lattr3.on_lights
+    assert point not in lattr3.on_lights
+    assert ambient not in lattr3.on_lights
+
+
+def test_lightattrib_compose_both():
+    # Tests a case in which a child node both enables and disables a light.
+    lattr1 = core.LightAttrib.make()
+    lattr1 = lattr1.add_on_light(spot)
+    lattr1 = lattr1.add_on_light(point)
+
+    lattr2 = core.LightAttrib.make()
+    lattr2 = lattr2.add_on_light(ambient)
+    lattr2 = lattr2.add_on_light(spot)
+    lattr2 = lattr2.add_off_light(point)
+
+    lattr3 = lattr1.compose(lattr2)
+    assert lattr3.get_num_on_lights() == 2
+
+    assert spot in lattr3.on_lights
+    assert point not in lattr3.on_lights
+    assert ambient in lattr3.on_lights
+
+
+def test_lightattrib_compose_alloff():
+    # Tests a case in which a child node disables all lights.
+    lattr1 = core.LightAttrib.make()
+    lattr1 = lattr1.add_on_light(spot)
+    lattr1 = lattr1.add_on_light(point)
+    assert lattr1.get_num_on_lights() == 2
+
+    lattr2 = core.LightAttrib.make_all_off()
+    assert lattr2.has_all_off()
+
+    lattr3 = lattr1.compose(lattr2)
+    assert lattr3.get_num_on_lights() == 0
+    assert lattr3.get_num_off_lights() == 0
+    assert lattr3.has_all_off()