diff --git a/rod3d.cc b/rod3d.cc
index c2bb42f305d53bca2a39eb64bdc5f1db1d46ae81..3ca6ab273bda0d4d3efd9e06553b828b1d68ff7b 100644
--- a/rod3d.cc
+++ b/rod3d.cc
@@ -183,7 +183,7 @@ int main (int argc, char *argv[]) try
     MatrixIndexSet indices(exactSolution.size(), exactSolution.size());
     rodAssembler.getNeighborsPerVertex(indices);
     indices.exportIdx(hessian);
-    rodAssembler.assembleMatrix(exactSolution, hessian);
+    rodAssembler.assembleMatrixFD(exactSolution, hessian);
 
 
     double error = std::numeric_limits<double>::max();