Only include <iosfwd> unless either EIGEN_DEBUG_ASSIGN is defined or we're in eigen2 support mode
diff --git a/test/vectorization_logic.cpp b/test/vectorization_logic.cpp
index ae99118..94a8a5c 100644
--- a/test/vectorization_logic.cpp
+++ b/test/vectorization_logic.cpp
@@ -22,6 +22,7 @@
 // License and a copy of the GNU General Public License along with
 // Eigen. If not, see <http://www.gnu.org/licenses/>.
 
+#define EIGEN_DEBUG_ASSIGN
 #include "main.h"
 #include <typeinfo>