diff --git a/opm/core/fluid/PvtPropertiesBasic.cpp b/opm/core/fluid/PvtPropertiesBasic.cpp
index 53b6cbfd..3d7d7bb2 100644
--- a/opm/core/fluid/PvtPropertiesBasic.cpp
+++ b/opm/core/fluid/PvtPropertiesBasic.cpp
@@ -60,8 +60,8 @@ namespace Opm
     }
 
     void PvtPropertiesBasic::init(const int num_phases,
-                                  const std::vector<double> rho,
-                                  const std::vector<double> mu)
+                                  const std::vector<double>& rho,
+                                  const std::vector<double>& visc)
     {
 	if (num_phases > 3 || num_phases < 1) {
 	    THROW("PvtPropertiesBasic::init() illegal num_phases: " << num_phases);
@@ -70,7 +70,7 @@ namespace Opm
 	formation_volume_factor_.clear();
 	formation_volume_factor_.resize(num_phases, 1.0);
         density_ = rho;
-        viscosity_ = mu;
+        viscosity_ = visc;
     }
 
     const double* PvtPropertiesBasic::surfaceDensities() const
diff --git a/opm/core/fluid/PvtPropertiesBasic.hpp b/opm/core/fluid/PvtPropertiesBasic.hpp
index 7bf234a7..d1a3e9f3 100644
--- a/opm/core/fluid/PvtPropertiesBasic.hpp
+++ b/opm/core/fluid/PvtPropertiesBasic.hpp
@@ -44,10 +44,11 @@ namespace Opm
 	///    mu1 [mu2, mu3]     (1.0)        Viscosity in cP
 	void init(const parameter::ParameterGroup& param);
 
-        /// Initialize from argument Basic  multi phase fluid pvt properties.
+        /// Initialize from arguments.
+        /// Basic multi phase fluid pvt properties.
         void init(const int num_phases,
-                  const std::vector<double> rho,
-                  const std::vector<double> mu);
+                  const std::vector<double>& rho,
+                  const std::vector<double>& visc);
 
         /// Number of active phases.
         int numPhases() const;