diff --git a/src/backends/x11/meta-barrier-x11.h b/src/backends/x11/meta-barrier-x11.h
index 802494c1f..9469fd86d 100644
--- a/src/backends/x11/meta-barrier-x11.h
+++ b/src/backends/x11/meta-barrier-x11.h
@@ -50,6 +50,8 @@ struct _MetaBarrierImplX11Class
   MetaBarrierImplClass parent_class;
 };
 
+GType meta_barrier_impl_x11_get_type (void) G_GNUC_CONST;
+
 MetaBarrierImpl *meta_barrier_impl_x11_new (MetaBarrier *barrier);
 
 G_END_DECLS