diff --git a/src/one-body-sample.cc b/src/one-body-sample.cc
index 72f47a00bbf43b33d77f35e6207d0f1cb26112ad..b959bfa3eb627956318722c285a85cf9a93c1873 100644
--- a/src/one-body-sample.cc
+++ b/src/one-body-sample.cc
@@ -44,6 +44,7 @@
 #include <dune/grid/utility/structuredgridfactory.hh>
 #include <dune/istl/bcrsmatrix.hh>
 #include <dune/istl/bvector.hh>
+#include <dune/istl/scaledidmatrix.hh>
 
 #include <dune/fufem/assemblers/functionalassembler.hh>
 #include <dune/fufem/assemblers/localassemblers/l2functionalassembler.hh>
@@ -240,7 +241,8 @@ int main(int argc, char *argv[]) {
 
       {
         MassAssembler<GridType, P1Basis::LocalFiniteElement,
-                      P1Basis::LocalFiniteElement, SmallMatrix> const localMass;
+                      P1Basis::LocalFiniteElement,
+                      Dune::ScaledIdentityMatrix<double, dims>> const localMass;
         OperatorAssembler<P1Basis, P1Basis>(p1Basis, p1Basis)
             .assemble(localMass, massMatrix);
         massMatrix *= density;