diff --git a/dune/solvers/common/numproc.hh b/dune/solvers/common/numproc.hh
index 6f0dc06e10b5fe9b765f15da0bd8dca08284e3fd..8b894db1c26d454f95e2fb28f93963e1277de2ae 100644
--- a/dune/solvers/common/numproc.hh
+++ b/dune/solvers/common/numproc.hh
@@ -30,6 +30,7 @@ class SolverError : public Dune::Exception {};
 
     };
 
+    inline
     std::istream& operator>>(std::istream &lhs, NumProc::VerbosityMode &e)
     {
         std::string s;