diff --git a/src/averagedistanceassembler.hh b/src/averagedistanceassembler.hh
index 198e9b2e788377658dc03c7c954e1119bdfd06fa..60ac52bb642f4425a822f3856aee0c27579cb8ed 100644
--- a/src/averagedistanceassembler.hh
+++ b/src/averagedistanceassembler.hh
@@ -19,8 +19,8 @@ class AverageDistanceAssembler<Rotation<3,double> >
 
 public:
 
-    AverageDistanceAssembler(const std::vector<TargetSpace> coefficients,
-                             const std::vector<double> weights)
+    AverageDistanceAssembler(const std::vector<TargetSpace>& coefficients,
+                             const std::vector<double>& weights)
         : coefficients_(coefficients),
           weights_(weights)
     {}