Index: trunk/data/validator/deprecated.mapcss
===================================================================
--- trunk/data/validator/deprecated.mapcss	(revision 7384)
+++ trunk/data/validator/deprecated.mapcss	(revision 7391)
@@ -251,2 +251,7 @@
   fixAdd: "leaf_cycle=deciduous";
 }
+
+*[natural=land] {
+  throwWarning: tr("{0}={1} is deprecated. Please use instead a multipolygon.", "{0.key}", "{0.value}");
+  assertMatch: "way natural=land";
+}