diff --git a/CMakeLists.txt b/CMakeLists.txt
index af27a769..72b0d161 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,6 +6,7 @@ project(xo_flatstring VERSION 1.0)
 enable_language(CXX)
 
 # common XO cmake macros (see proj/xo-cmake)
+include(GNUInstallDirs)
 include(cmake/xo-bootstrap-macros.cmake)
 
 # ----------------------------------------------------------------
diff --git a/cmake/xo-bootstrap-macros.cmake b/cmake/xo-bootstrap-macros.cmake
index 83f4a39b..1542d355 100644
--- a/cmake/xo-bootstrap-macros.cmake
+++ b/cmake/xo-bootstrap-macros.cmake
@@ -15,7 +15,7 @@ if (("${CMAKE_MODULE_PATH}" STREQUAL "") OR ("${CMAKE_MODULE_PATH}" STREQUAL pre
 endif()
 
 if (NOT XO_SUBMODULE_BUILD)
-    message("-- GUESSED_CMAKE_CMD=cmake -DCMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD} -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX} -DCMAKE_MODULE_PATH=${CMAKE_MODULE_PATH} -DCMAKE_PREFIX_PATH=${CMAKE_PREFIX_PATH} -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE} -B ${CMAKE_BINARY_DIR}")
+    message("-- GUESSED_CMAKE_CMD=cmake -DCMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD} -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX} -DCMAKE_MODULE_PATH=${CMAKE_MODULE_PATH} -DCMAKE_PREFIX_PATH=${CMAKE_PREFIX_PATH} -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE} -DCMAKE_INSTALL_DOCDIR=${CMAKE_INSTALL_DOCDIR} -B ${CMAKE_BINARY_DIR}")
     message("-- CMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}")
     message("-- CMAKE_MODULE_PATH=${CMAKE_MODULE_PATH}")
 endif()
diff --git a/docs/CMakeLists.txt b/docs/CMakeLists.txt
index c6fcc37b..b31549e0 100644
--- a/docs/CMakeLists.txt
+++ b/docs/CMakeLists.txt
@@ -94,12 +94,15 @@ else()
     # - html docs generated in build/docs/sphinx
     # - copy the doc tree to share/doc/xo_unit/html
     #
+    #  DESTINATION: CMAKE_INSTALL_DOCDIR
+    #                => DATAROOTDIR/doc/PROJECT_NAME
+    #                => CMAKE_INSTALL_PREFIX/share/doc/xo_flatstring
     #  OPTIONAL:    install directory tree if it exists,
     #               but don't complain if it's missing
     install(
         DIRECTORY ${SPHINX_OUTPUT_DIR}
         FILE_PERMISSIONS OWNER_READ GROUP_READ WORLD_READ
-        DESTINATION ${CMAKE_INSTALL_PREFIX}/share/doc/${PROJECT_NAME}
+        DESTINATION ${CMAKE_INSTALL_DOCDIR}
         COMPONENT Documentation
         OPTIONAL)