diff --git a/dune/solvers/solvers/quadraticipopt.hh b/dune/solvers/solvers/quadraticipopt.hh
index 7649012b9d512b82f66c0f9121ed4e2f83c9e49b..f51e391544c62cd988d841d42d6b284a2663379e 100644
--- a/dune/solvers/solvers/quadraticipopt.hh
+++ b/dune/solvers/solvers/quadraticipopt.hh
@@ -156,6 +156,9 @@ bool QuadraticIPOptProblem<MatrixType,VectorType>::
 get_nlp_info(Ipopt::Index& n, Ipopt::Index& m, Ipopt::Index& nnz_jac_g,
              Ipopt::Index& nnz_h_lag, Ipopt::TNLP::IndexStyleEnum& index_style)
 {
+    // use the C style indexing (0-based)
+    index_style = Ipopt::TNLP::C_STYLE;
+
     // Number of variables
     n = x_->dim();