diff --git a/ql/pricingengines/barrier/analyticpartialtimebarrieroptionengine.cpp b/ql/pricingengines/barrier/analyticpartialtimebarrieroptionengine.cpp
index 2b501413053..08f9ab5ca82 100644
--- a/ql/pricingengines/barrier/analyticpartialtimebarrieroptionengine.cpp
+++ b/ql/pricingengines/barrier/analyticpartialtimebarrieroptionengine.cpp
@@ -32,8 +32,8 @@ namespace QuantLib {
     }
 
     Real AnalyticPartialTimeBarrierOptionEngine::calculate(PartialTimeBarrierOption::arguments& arguments,
-                                                          ext::shared_ptr<PlainVanillaPayoff> payoff,
-                                                          ext::shared_ptr<GeneralizedBlackScholesProcess> process) const {
+                                                          const ext::shared_ptr<PlainVanillaPayoff>& payoff,
+                                                          const ext::shared_ptr<GeneralizedBlackScholesProcess>& process) const {
         Barrier::Type barrierType = arguments.barrierType;
         PartialBarrier::Range barrierRange = arguments.barrierRange;
         Rate r = process->riskFreeRate()->zeroRate(residualTime(), Continuous,
diff --git a/ql/pricingengines/barrier/analyticpartialtimebarrieroptionengine.hpp b/ql/pricingengines/barrier/analyticpartialtimebarrieroptionengine.hpp
index 78bf55007f3..b08c7cad14c 100644
--- a/ql/pricingengines/barrier/analyticpartialtimebarrieroptionengine.hpp
+++ b/ql/pricingengines/barrier/analyticpartialtimebarrieroptionengine.hpp
@@ -45,8 +45,8 @@ namespace QuantLib {
       private:
         ext::shared_ptr<GeneralizedBlackScholesProcess> process_;
         Real calculate(PartialTimeBarrierOption::arguments& arguments,
-                      ext::shared_ptr<PlainVanillaPayoff> payoff, 
-                      ext::shared_ptr<GeneralizedBlackScholesProcess> process) const;
+                      const ext::shared_ptr<PlainVanillaPayoff>& payoff, 
+                      const ext::shared_ptr<GeneralizedBlackScholesProcess>& process) const;
         Real underlying() const;
         Time residualTime() const;
         Time coverEventTime() const;