--- freecad-0.17/CMakeLists.txt
+++ freecad-0.17/CMakeLists.txt
@@ -146,9 +146,15 @@
 #IGNORE     SET(CMAKE_INSTALL_PREFIX "/usr/lib${LIB_SUFFIX}/freecad" CACHE PATH "Installation root directory")
 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)
 # Don't set it without manual adaption of LibDir variable in src/App/FreeCADInit.py
 SET(CMAKE_INSTALL_LIBDIR lib CACHE PATH "Output directory for libraries")