diff --git a/dune/istl/bcrsmatrix.hh b/dune/istl/bcrsmatrix.hh
index 5304f18d0af58895605885263be9a0a1be5f28ab..baff3c9e51d5ac6d362eaa57368a73e5e63537ea 100644
--- a/dune/istl/bcrsmatrix.hh
+++ b/dune/istl/bcrsmatrix.hh
@@ -768,7 +768,7 @@ namespace Dune {
       if (_nnz<=0)
       {
         _nnz = 0;
-        for (size_type i=0; i<n; i++)
+        for (size_type i=0; i<Mat.n; i++)
           _nnz += Mat.r[i].getsize();
       }