Index: trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/ExpressionFactory.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/ExpressionFactory.java	(revision 17914)
+++ trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/ExpressionFactory.java	(revision 17916)
@@ -228,5 +228,5 @@
         FACTORY_MAP.put("rgba", Factory.of(float.class, float.class, float.class, float.class, Functions::rgba));
         FACTORY_MAP.put("role", Factory.ofEnv(Functions::role));
-        FACTORY_MAP.put("round", Factory.of(Math::acos));
+        FACTORY_MAP.put("round", Factory.of(Math::round));
         FACTORY_MAP.put("setting", Factory.ofEnv(String.class, Functions::setting));
         FACTORY_MAP.put("signum", Factory.of(Math::signum));