diff --git a/gio/tests/contenttype.c b/gio/tests/contenttype.c
index 407186b6b..4b4be46a1 100644
--- a/gio/tests/contenttype.c
+++ b/gio/tests/contenttype.c
@@ -144,6 +144,7 @@ test_subtype (void)
   xml = g_content_type_from_mime_type ("application/xml");
 
   g_assert (g_content_type_is_a (xml, plain));
+  g_assert (g_content_type_is_mime_type (xml, plain));
 
   g_free (plain);
   g_free (xml);