diff --git a/poky/meta/lib/oe/spdx.py b/poky/meta/lib/oe/spdx.py
index 9e7ced5..14ca706 100644
--- a/poky/meta/lib/oe/spdx.py
+++ b/poky/meta/lib/oe/spdx.py
@@ -105,10 +105,13 @@
                 obj._spdx[name] = []
             return obj._spdx[name]
 
+        def set_helper(obj, value):
+            obj._spdx[name] = list(value)
+
         def del_helper(obj):
             del obj._spdx[name]
 
-        attrs[name] = property(get_helper, None, del_helper)
+        attrs[name] = property(get_helper, set_helper, del_helper)
 
     def init(self, source):
         return [self.prop.init(o) for o in source]