diff --git a/src/one-body-sample.cc b/src/one-body-sample.cc
index 91458ad6b1aa9e01e9b98c403f385f9b7518d473..c1d1c872389e03e0bf1e66c6eccd03a821c1ce5a 100644
--- a/src/one-body-sample.cc
+++ b/src/one-body-sample.cc
@@ -240,7 +240,7 @@ int main(int argc, char *argv[]) {
 
       {
         MassAssembler<GridType, P1Basis::LocalFiniteElement,
-                      P1Basis::LocalFiniteElement> const localMass;
+                      P1Basis::LocalFiniteElement, SmallMatrix> const localMass;
         OperatorAssembler<P1Basis, P1Basis>(p1Basis, p1Basis)
             .assemble(localMass, massMatrix);
         massMatrix *= density;