diff --git a/test/formats/common.py b/test/formats/common.py
index f5a0e67a5..705f21c3b 100644
--- a/test/formats/common.py
+++ b/test/formats/common.py
@@ -223,6 +223,7 @@ class CommonTests:
             metadata = Metadata(tags)
             loaded_metadata = save_and_load_metadata(self.filename, metadata)
             for tag in tags:
+                self.assertFalse(self.format.supports_tag(tag))
                 self.assertTrue(tag not in loaded_metadata, '%s: %r != None' % (tag, loaded_metadata[tag]))
 
     class TagFormatsTestCase(SimpleFormatsTestCase):