diff --git a/test/mpl2only.cpp b/test/mpl2only.cpp
index 7d04d6bba..296350d08 100644
--- a/test/mpl2only.cpp
+++ b/test/mpl2only.cpp
@@ -7,7 +7,9 @@
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+#ifndef EIGEN_MPL2_ONLY
 #define EIGEN_MPL2_ONLY
+#endif
 #include <Eigen/Dense>
 #include <Eigen/SparseCore>
 #include <Eigen/SparseLU>