diff -rupN eigen-eigen-323c052e1731/CMakeLists.txt eigen-eigen-323c052e1731-new/CMakeLists.txt
--- eigen-eigen-323c052e1731/CMakeLists.txt	2018-12-25 23:10:48.592420583 +0100
+++ eigen-eigen-323c052e1731-new/CMakeLists.txt	2018-12-25 23:10:48.659420305 +0100
@@ -531,7 +531,7 @@ set ( EIGEN_VERSION_MAJOR  ${EIGEN_WORLD
 set ( EIGEN_VERSION_MINOR  ${EIGEN_MAJOR_VERSION} )
 set ( EIGEN_VERSION_PATCH  ${EIGEN_MINOR_VERSION} )
 set ( EIGEN_DEFINITIONS "")
-set ( EIGEN_INCLUDE_DIR "${CMAKE_INSTALL_PREFIX}/${INCLUDE_INSTALL_DIR}" )
+set ( EIGEN_INCLUDE_DIR ${INCLUDE_INSTALL_DIR} )
 set ( EIGEN_ROOT_DIR ${CMAKE_INSTALL_PREFIX} )
 
 # Interface libraries require at least CMake 3.0