Index: trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/MapCSSStyleSource.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/MapCSSStyleSource.java	(revision 7122)
+++ trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/MapCSSStyleSource.java	(revision 7124)
@@ -10,4 +10,5 @@
 import java.io.InputStream;
 import java.nio.charset.StandardCharsets;
+import java.text.MessageFormat;
 import java.util.ArrayList;
 import java.util.List;
@@ -126,5 +127,6 @@
             }
             MapCSSRule optRule = new MapCSSRule(r.selector.optimizedBaseCheck(), r.declaration);
-            switch (((GeneralSelector) selRightmost).getBase()) {
+            final String base = ((GeneralSelector) selRightmost).getBase();
+            switch (base) {
                 case "node":
                     nodeRules.add(optRule);
@@ -149,4 +151,9 @@
                 case "canvas":
                     canvasRules.add(r);
+                default:
+                    final RuntimeException e = new RuntimeException(MessageFormat.format("Unknown MapCSS base selector {0}", base));
+                    Main.warn(tr("Failed to parse Mappaint styles from ''{0}''. Error was: {1}", url, e.getMessage()));
+                    Main.error(e);
+                    logError(e);
             }
         }