diff --git a/source/net/yacy/cora/federate/solr/Ranking.java b/source/net/yacy/cora/federate/solr/Ranking.java
index ee82c887d..5814533fe 100644
--- a/source/net/yacy/cora/federate/solr/Ranking.java
+++ b/source/net/yacy/cora/federate/solr/Ranking.java
@@ -177,6 +177,7 @@ public class Ranking {
      * @return
      */
     public String getBoostFunction() {
+        if (this.boostFunction.contains("last_modified")) return ""; // since solr 5.0 this does not work any more
         return this.boostFunction;
     }