Index: trunk/data/validator/deprecated.mapcss
===================================================================
--- trunk/data/validator/deprecated.mapcss	(revision 8023)
+++ trunk/data/validator/deprecated.mapcss	(revision 8121)
@@ -392,2 +392,8 @@
   throwWarning: tr("Unspecific tag {0}", "{0.tag}");
 }
+
+/* unclear definition, see #11183 */
+*[sport=skiing][!piste:type] {
+  throwWarning: tr("Definition of {0} is unclear", "{0.tag}");
+  suggestAlternative: {1.key};
+}