diff --git a/arangod/Aql/TraversalNode.cpp b/arangod/Aql/TraversalNode.cpp
index 86cf366096..02ac13a3cc 100644
--- a/arangod/Aql/TraversalNode.cpp
+++ b/arangod/Aql/TraversalNode.cpp
@@ -311,7 +311,10 @@ void TraversalNode::toJsonHelper (triagens::basics::Json& nodes,
                                                                       map.second.size());
       for (auto const & x : map.second) {
         triagens::basics::Json exp(zone, triagens::basics::Json::Object);
-        x->toJson(exp, zone);
+        auto tmp = dynamic_cast<SimpleTraverserExpression*>(x);
+        if (tmp != nullptr) {
+          tmp->toJson(exp, zone);
+        }
         expressionArray(exp);
       }
       expressionObject.set(std::to_string(map.first), expressionArray);
diff --git a/arangod/VocBase/Traverser.h b/arangod/VocBase/Traverser.h
index 95df4568c9..d9947766b7 100644
--- a/arangod/VocBase/Traverser.h
+++ b/arangod/VocBase/Traverser.h
@@ -125,8 +125,8 @@ namespace triagens {
             }
           }
 
-          virtual void toJson (triagens::basics::Json& json,
-                               TRI_memory_zone_t* zone) const;
+          void toJson (triagens::basics::Json& json,
+                       TRI_memory_zone_t* zone) const;
 
           bool matchesCheck (TRI_doc_mptr_t& element,
                              TRI_document_collection_t* collection,