Index: trunk/data/validator/combinations.mapcss
===================================================================
--- trunk/data/validator/combinations.mapcss	(revision 8076)
+++ trunk/data/validator/combinations.mapcss	(revision 8077)
@@ -84,4 +84,6 @@
 
 /* {0.key} without {1.key} (info level) */
+*[lanes:forward][!lanes:backward][oneway!=yes][oneway!=-1],
+*[lanes:backward][!lanes:forward][oneway!=yes][oneway!=-1],
 *[leaf_type ][!leaf_cycle],
 *[leaf_cycle][!leaf_type] {
@@ -148,4 +150,12 @@
 }
 
+/* {0.tag} together with {1.key}, see #9389 */
+*[oneway=yes][/:backward/],
+*[oneway=yes][/:forward/],
+*[oneway=-1 ][/:backward/],
+*[oneway=-1 ][/:forward/] {
+  throwWarning: tr("{0} together with {1}", "{0.tag}", "{1.key}");
+}
+
 /* {0.tag} together with {1.tag} (info level), see #9696 */
 *[highway=footway][oneway=no] {