--- CMakeLists.txt	2014-01-06 13:46:44.516313646 +0100
+++ CMakeLists.txt.new	2014-01-06 13:58:16.035280554 +0100
@@ -69,9 +69,15 @@
     SET(INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/lib")
 endif(WIN32)
 
-SET(CMAKE_INSTALL_DATADIR data CACHE PATH "Output directory for data and resource files")
-SET(CMAKE_INSTALL_INCLUDEDIR include CACHE PATH "Output directory for header files")
-SET(CMAKE_INSTALL_DOCDIR doc CACHE PATH "Output directory for documentation and license files")
+if(NOT CMAKE_INSTALL_DATADIR)
+	SET(CMAKE_INSTALL_DATADIR data CACHE PATH "Output directory for data and resource files")
+endif(NOT CMAKE_INSTALL_DATADIR)
+if(NOT CMAKE_INSTALL_INCLUDEDIR)
+	SET(CMAKE_INSTALL_INCLUDEDIR include CACHE PATH "Output directory for header files")
+endif(NOT CMAKE_INSTALL_INCLUDEDIR)
+if(NOT CMAKE_INSTALL_DOCDIR)
+	SET(CMAKE_INSTALL_DOCDIR doc CACHE PATH "Output directory for documentation and license files")
+endif(NOT CMAKE_INSTALL_DOCDIR)
 
 # used as compiler defines
 SET(RESOURCEDIR "${CMAKE_INSTALL_DATADIR}")