diff --git a/dune/matrix-vector/singlenonzerocolumnmatrix.hh b/dune/matrix-vector/singlenonzerocolumnmatrix.hh
index afe07c8cd0190ab3047852546cbf245859a1289e..4225019a27c2ee06fbebd710d55e05a5c9d0dad2 100644
--- a/dune/matrix-vector/singlenonzerocolumnmatrix.hh
+++ b/dune/matrix-vector/singlenonzerocolumnmatrix.hh
@@ -84,7 +84,7 @@ public:
     void umtv(const X& x, Y& y) const
     {
         for(size_type i=0; i<N(); ++i)
-            y[columnIndex_] = nonZeroColumn_[i] * x[i];
+            y[columnIndex_] += nonZeroColumn_[i] * x[i];
     }
 
     template<class X , class Y >