diff --git a/istl/bdmatrix.hh b/istl/bdmatrix.hh
index 6ac33b91f3d276af33c09ba90e12d97fcdd28b36..e3c587097316c11e2ebf6f6844e3fdd3eeb92cd0 100644
--- a/istl/bdmatrix.hh
+++ b/istl/bdmatrix.hh
@@ -47,6 +47,9 @@ namespace Dune {
     /** \brief Get the i-th diagonal element */
     B& operator[](int i) {return data_[i];}
 
+    /** \brief Get the i-th diagonal element */
+    const B& operator[](int i) const {return data_[i];}
+
     /** \brief y += Ax */
     template <class X, class Y>
     void umv(const X& x, Y& y) const {