diff --git a/gio/Gio.metadata b/gio/Gio.metadata
index b80aa5712..59a390dc1 100644
--- a/gio/Gio.metadata
+++ b/gio/Gio.metadata
@@ -30,6 +30,8 @@
   <attr path="/api/namespace/interface[@cname='GIcon']" name="consume_only">1</attr>
   <attr path="/api/namespace/interface[@cname='GMount']" name="consume_only">1</attr>
   <attr path="/api/namespace/interface[@cname='GMount']/method[@name='CanUnmount']" name="name">GetCanUnmount</attr>
+  <attr path="/api/namespace/interface[@cname='GMount']/method[@name='GuessContentTypeFinish']/return-type" name="null_term_array">1</attr>
+  <attr path="/api/namespace/interface[@cname='GMount']/method[@name='GuessContentTypeSync']/return-type" name="null_term_array">1</attr>
   <attr path="/api/namespace/interface[@cname='GSeekable']/method[@cname='g_seekable_can_seek']" name="name">GetCanSeek</attr>
   <attr path="/api/namespace/interface[@cname='GSeekable']/method[@cname='g_seekable_tell']" name="name">GetPosition</attr>
   <attr path="/api/namespace/interface[@cname='GTlsServerConnection']/property[@cname='authentication-mode']" name="hidden">1</attr>