Index: trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/MapCSSRuleIndex.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/MapCSSRuleIndex.java	(revision 18445)
+++ trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/MapCSSRuleIndex.java	(revision 18451)
@@ -5,4 +5,5 @@
 import java.util.BitSet;
 import java.util.Collections;
+import java.util.EnumSet;
 import java.util.HashMap;
 import java.util.Iterator;
@@ -121,4 +122,8 @@
     }
 
+    /** Valid key types for indexing (see {@link ConditionFactory.KeyMatchType}) */
+    private static final EnumSet<ConditionFactory.KeyMatchType> VALID_INDEX_KEY_TYPES = EnumSet.of(
+            ConditionFactory.KeyMatchType.EQ, ConditionFactory.KeyMatchType.TRUE, ConditionFactory.KeyMatchType.FALSE);
+
     /**
      * All rules this index is for. Once this index is built, this list is sorted.
@@ -187,5 +192,5 @@
         String key = null;
         for (Condition c : conds) {
-            if (c instanceof KeyCondition) {
+            if (c instanceof KeyCondition && VALID_INDEX_KEY_TYPES.contains(((KeyCondition) c).matchType)) {
                 KeyCondition keyCondition = (KeyCondition) c;
                 if (!keyCondition.negateResult) {