diff --git a/dune/tectonic/localfriction.hh b/dune/tectonic/localfriction.hh
index b9cded4b4cd785dc32b522531f8707cf3fa36061..4f610b255f285941fb52ec36fa68d4045b30854f 100644
--- a/dune/tectonic/localfriction.hh
+++ b/dune/tectonic/localfriction.hh
@@ -19,7 +19,7 @@ template <int dimension> class LocalFriction {
   using VectorType = FieldVector<double, dimension>;
   using MatrixType = FieldMatrix<double, dimension, dimension>;
 
-  LocalFriction(shared_ptr<FrictionPotentialWrapper> func)
+  explicit LocalFriction(shared_ptr<FrictionPotentialWrapper> func)
       : func(func), smp(func->smallestPositivePoint()) {}
 
   double operator()(VectorType const &x) const {