diff --git a/opm/core/simulator/WellState.hpp b/opm/core/simulator/WellState.hpp
index 197a8226..acadf7ef 100644
--- a/opm/core/simulator/WellState.hpp
+++ b/opm/core/simulator/WellState.hpp
@@ -213,7 +213,7 @@ namespace Opm
             return wellRates().size() / numWells();
         }
 
-        virtual data::Wells report(const PhaseUsage &pu) const
+        virtual data::Wells report(const PhaseUsage&) const
         {
             return { { /* WellState offers no completion data, so that has to be added later */ },
                 this->bhp(),