diff -up ./mrpt-0.9.6/libs/base/include/mrpt/math/eigen_plugins.h.eigen306 ./mrpt-0.9.6/libs/base/include/mrpt/math/eigen_plugins.h
--- ./mrpt-0.9.6/libs/base/include/mrpt/math/eigen_plugins.h.eigen306	2012-08-20 20:43:26.741089478 -0400
+++ ./mrpt-0.9.6/libs/base/include/mrpt/math/eigen_plugins.h	2012-08-20 20:43:48.993922110 -0400
@@ -25,7 +25,8 @@
    |     along with MRPT.  If not, see <http://www.gnu.org/licenses/>.         |
    |                                                                           |
    +---------------------------------------------------------------------------+ */
-
+#ifndef EIGEN_PLUGIN_H
+#define EIGEN_PLUGIN_H
 // -------------------------------------------------------------------------
 // Note: This file will be included within the body of Eigen::MatrixBase
 // -------------------------------------------------------------------------
@@ -862,4 +863,4 @@ public:
 			for (size_t dst_col_blk=0;dst_col_blk<N; ++dst_col_blk )
 				out.coeffRef(dst_row_blk,dst_col_blk) = this->coeff(indices[dst_row_blk],indices[dst_col_blk]);
 	}
-
+#endif