Index: trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/Instruction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/Instruction.java	(revision 17769)
+++ trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/Instruction.java	(revision 17770)
@@ -10,4 +10,5 @@
 import org.openstreetmap.josm.gui.mappaint.MapPaintStyles.IconReference;
 import org.openstreetmap.josm.gui.mappaint.StyleKeys;
+import org.openstreetmap.josm.tools.Logging;
 
 /**
@@ -91,5 +92,10 @@
             Object value;
             if (val instanceof Expression) {
-                value = ((Expression) val).evaluate(env);
+                try {
+                    value = ((Expression) val).evaluate(env);
+                } catch (RuntimeException ex) {
+                    Logging.error(ex);
+                    value = null;
+                }
             } else {
                 value = val;