Yuri <ydewit <at> gmail.com> writes: The workaround that worked for me was to use a function: salience ( -1 * FN.priority(c.size, c.size) ) (Using "-1 *" because just "-" does not work) Here is the exception: java.lang.ClassCastException: java.lang.Double at org.drools.base.mvel.MVELSalienceExpression .getValue(MVELSalienceExpression.java:33)