diff --git a/CMakeLists.txt b/CMakeLists.txt
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,6 +4,7 @@
 PROJECT(${PROJECT_NAME})
 
 INCLUDE(FindPythonInterp)
+INCLUDE(FindWget)
 
 IF(EXISTS ${PROJECT_SOURCE_DIR}/cmake/version.cmake)
   INCLUDE(${PROJECT_SOURCE_DIR}/cmake/version.cmake)
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()
diff --git a/doc/Doxyfile.in b/doc/Doxyfile.in
--- a/doc/Doxyfile.in
+++ b/doc/Doxyfile.in
@@ -225,7 +225,7 @@
 #---------------------------------------------------------------------------
 # Options related to the search engine   
 #---------------------------------------------------------------------------
-TAGFILES               = "@abs_top_srcdir@/doc/libstdc++.tag = http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/  "
+TAGFILES               = "@abs_top_builddir@/doc/libstdc++.tag = http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/  "
 GENERATE_TAGFILE       = html/lemon.tag
 ALLEXTERNALS           = NO
 EXTERNAL_GROUPS        = NO