diff --git a/doc/CMakeLists.txt b/doc/CMakeLists.txt
--- a/doc/CMakeLists.txt
+++ b/doc/CMakeLists.txt
@@ -54,3 +54,15 @@
   ENDIF()
 
 ENDIF()
+
+IF(WGET_FOUND)
+ADD_CUSTOM_TARGET(update-external-tags
+  COMMAND ${CMAKE_COMMAND} -E make_directory dl
+  # COMMAND ${CMAKE_COMMAND} -E copy libstdc++.tag dl
+  COMMAND ${WGET_EXECUTABLE} wget -P dl -N libstdc++.tag.tmp http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/libstdc++.tag
+  COMMAND ${CMAKE_COMMAND} -E rename dl/libstdc++.tag libstdc++.tag
+  COMMAND ${CMAKE_COMMAND} -E remove dl/libstdc++.tag
+  COMMAND ${CMAKE_COMMAND} -E remove_directory dl
+  WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+  )
+ENDIF()