--- /dev/null
+diff --git a/CMakeLists_Directories.cmake b/CMakeLists_Directories.cmake
+index db6133f..faf85ce 100644
+--- a/CMakeLists_Directories.cmake
++++ b/CMakeLists_Directories.cmake
+@@ -36,14 +36,16 @@ else()
+ endif()
+
+ #SHARE - use the default on Apple as TAG_VERSION is empty
+-if(WIN32 OR OS2)
+- set(DOCDIR "${CMAKE_INSTALL_DATAROOTDIR}/doc/")
+-elseif(TAG_VERSION OR BUILD_OSX_BUNDLE)
+- set(DOCDIR "${CMAKE_INSTALL_DATAROOTDIR}/doc/${MAIN_DIR_NAME}${TAG_VERSION}/")
+-elseif(NOT WANT_VERSIONING)
+- set(DOCDIR "${CMAKE_INSTALL_DATAROOTDIR}/doc/${MAIN_DIR_NAME}/")
+-else()
+- set(DOCDIR "${CMAKE_INSTALL_DATAROOTDIR}/doc/${MAIN_DIR_NAME}-${VERSION}/")
++if(NOT DOCDIR)
++ if(WIN32 OR OS2)
++ set(DOCDIR "${CMAKE_INSTALL_DATAROOTDIR}/doc/")
++ elseif(TAG_VERSION OR BUILD_OSX_BUNDLE)
++ set(DOCDIR "${CMAKE_INSTALL_DATAROOTDIR}/doc/${MAIN_DIR_NAME}${TAG_VERSION}/")
++ elseif(NOT WANT_VERSIONING)
++ set(DOCDIR "${CMAKE_INSTALL_DATAROOTDIR}/doc/${MAIN_DIR_NAME}/")
++ else()
++ set(DOCDIR "${CMAKE_INSTALL_DATAROOTDIR}/doc/${MAIN_DIR_NAME}-${VERSION}/")
++ endif()
+ endif()
+
+ if(IS_ABSOLUTE ${DOCDIR} AND WANT_RELOCATABLE)