diff --git a/Modules/ExternalProject.cmake b/Modules/ExternalProject.cmake
index 301d1fc4d..0353e4562 100644
--- a/Modules/ExternalProject.cmake
+++ b/Modules/ExternalProject.cmake
@@ -252,12 +252,23 @@ define_property(DIRECTORY PROPERTY "EP_STEP_TARGETS" INHERITED
   )
 
 
-function(_ep_write_gitclone_script script_filename source_dir git_EXECUTABLE git_repository git_tag src_name work_dir)
+function(_ep_write_gitclone_script script_filename source_dir git_EXECUTABLE git_repository git_tag src_name work_dir gitclone_infofile gitclone_stampfile)
   file(WRITE ${script_filename}
 "if(\"${git_tag}\" STREQUAL \"\")
   message(FATAL_ERROR \"Tag for git checkout should not be empty.\")
 endif()
 
+set(run 0)
+
+if(\"${gitclone_infofile}\" IS_NEWER_THAN \"${gitclone_stampfile}\")
+  set(run 1)
+endif()
+
+if(NOT run)
+  message(STATUS \"Avoiding repeated git clone, stamp file is up to date: '${gitclone_stampfile}'\")
+  return()
+endif()
+
 execute_process(
   COMMAND \${CMAKE_COMMAND} -E remove_directory \"${source_dir}\"
   RESULT_VARIABLE error_code
@@ -302,6 +313,19 @@ if(error_code)
   message(FATAL_ERROR \"Failed to update submodules in: '${work_dir}/${src_name}'\")
 endif()
 
+# Complete success, update the script-last-run stamp file:
+#
+execute_process(
+  COMMAND \${CMAKE_COMMAND} -E copy
+    \"${gitclone_infofile}\"
+    \"${gitclone_stampfile}\"
+  WORKING_DIRECTORY \"${work_dir}/${src_name}\"
+  RESULT_VARIABLE error_code
+  )
+if(error_code)
+  message(FATAL_ERROR \"Failed to copy script-last-run stamp file: '${gitclone_stampfile}'\")
+endif()
+
 "
 )
 
@@ -824,15 +848,23 @@ function(_ep_get_configuration_subdir_suffix suffix_var)
 endfunction(_ep_get_configuration_subdir_suffix)
 
 
+function(_ep_get_step_stampfile name step stampfile_var)
+  ExternalProject_Get_Property(${name} stamp_dir)
+
+  _ep_get_configuration_subdir_suffix(cfgdir)
+  set(stampfile "${stamp_dir}${cfgdir}/${name}-${step}")
+
+  set(${stampfile_var} "${stampfile}" PARENT_SCOPE)
+endfunction()
+
+
 function(ExternalProject_Add_StepTargets name)
   set(steps ${ARGN})
 
-  _ep_get_configuration_subdir_suffix(cfgdir)
-  ExternalProject_Get_Property(${name} stamp_dir)
-
   foreach(step ${steps})
+    _ep_get_step_stampfile(${name} ${step} stamp_file)
     add_custom_target(${name}-${step}
-      DEPENDS ${stamp_dir}${cfgdir}/${name}-${step})
+      DEPENDS ${stamp_file})
 
     # Depend on other external projects (target-level).
     get_property(deps TARGET ${name} PROPERTY _EP_DEPENDS)
@@ -845,23 +877,26 @@ endfunction(ExternalProject_Add_StepTargets)
 
 function(ExternalProject_Add_Step name step)
   set(cmf_dir ${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles)
-  ExternalProject_Get_Property(${name} stamp_dir)
-
   _ep_get_configuration_subdir_suffix(cfgdir)
 
+  set(complete_stamp_file "${cmf_dir}${cfgdir}/${name}-complete")
+  _ep_get_step_stampfile(${name} ${step} stamp_file)
+
   add_custom_command(APPEND
-    OUTPUT ${cmf_dir}${cfgdir}/${name}-complete
-    DEPENDS ${stamp_dir}${cfgdir}/${name}-${step}
+    OUTPUT ${complete_stamp_file}
+    DEPENDS ${stamp_file}
     )
+
   _ep_parse_arguments(ExternalProject_Add_Step
-                       ${name} _EP_${step}_ "${ARGN}")
+                      ${name} _EP_${step}_ "${ARGN}")
 
   # Steps depending on this step.
   get_property(dependers TARGET ${name} PROPERTY _EP_${step}_DEPENDERS)
   foreach(depender IN LISTS dependers)
+    _ep_get_step_stampfile(${name} ${depender} depender_stamp_file)
     add_custom_command(APPEND
-      OUTPUT ${stamp_dir}${cfgdir}/${name}-${depender}
-      DEPENDS ${stamp_dir}${cfgdir}/${name}-${step}
+      OUTPUT ${depender_stamp_file}
+      DEPENDS ${stamp_file}
       )
   endforeach()
 
@@ -871,7 +906,8 @@ function(ExternalProject_Add_Step name step)
   # Dependencies on steps.
   get_property(dependees TARGET ${name} PROPERTY _EP_${step}_DEPENDEES)
   foreach(dependee IN LISTS dependees)
-    list(APPEND depends ${stamp_dir}${cfgdir}/${name}-${dependee})
+    _ep_get_step_stampfile(${name} ${dependee} dependee_stamp_file)
+    list(APPEND depends ${dependee_stamp_file})
   endforeach()
 
   # The command to run.
@@ -901,10 +937,10 @@ function(ExternalProject_Add_Step name step)
   # Run every time?
   get_property(always TARGET ${name} PROPERTY _EP_${step}_ALWAYS)
   if(always)
-    set_property(SOURCE ${stamp_dir}${cfgdir}/${name}-${step} PROPERTY SYMBOLIC 1)
+    set_property(SOURCE ${stamp_file} PROPERTY SYMBOLIC 1)
     set(touch)
   else()
-    set(touch ${CMAKE_COMMAND} -E touch ${stamp_dir}${cfgdir}/${name}-${step})
+    set(touch ${CMAKE_COMMAND} -E touch ${stamp_file})
   endif()
 
   # Wrap with log script?
@@ -914,7 +950,7 @@ function(ExternalProject_Add_Step name step)
   endif()
 
   add_custom_command(
-    OUTPUT ${stamp_dir}${cfgdir}/${name}-${step}
+    OUTPUT ${stamp_file}
     COMMENT ${comment}
     COMMAND ${command}
     COMMAND ${touch}
@@ -1079,9 +1115,15 @@ function(_ep_add_download_command name)
       set(git_tag "master")
     endif()
 
+    # For the download step, and the git clone operation, only the repository
+    # should be recorded in a configured RepositoryInfo file. If the repo
+    # changes, the clone script should be run again. But if only the tag
+    # changes, avoid running the clone script again. Let the 'always' running
+    # update step checkout the new tag.
+    #
     set(repository ${git_repository})
     set(module)
-    set(tag ${git_tag})
+    set(tag)
     configure_file(
       "${CMAKE_ROOT}/Modules/RepositoryInfo.txt.in"
       "${stamp_dir}/${name}-gitinfo.txt"
@@ -1097,6 +1139,7 @@ function(_ep_add_download_command name)
     #
     _ep_write_gitclone_script(${tmp_dir}/${name}-gitclone.cmake ${source_dir}
       ${GIT_EXECUTABLE} ${git_repository} ${git_tag} ${src_name} ${work_dir}
+      ${stamp_dir}/${name}-gitinfo.txt ${stamp_dir}/${name}-gitclone-lastrun.txt
       )
     set(comment "Performing download step (git clone) for '${name}'")
     set(cmd ${CMAKE_COMMAND} -P ${tmp_dir}/${name}-gitclone.cmake)
@@ -1277,14 +1320,12 @@ endfunction(_ep_add_patch_command)
 function(_ep_add_configure_command name)
   ExternalProject_Get_Property(${name} source_dir binary_dir tmp_dir)
 
-  _ep_get_configuration_subdir_suffix(cfgdir)
-
   # Depend on other external projects (file-level).
   set(file_deps)
   get_property(deps TARGET ${name} PROPERTY _EP_DEPENDS)
   foreach(dep IN LISTS deps)
-    get_property(dep_stamp_dir TARGET ${dep} PROPERTY _EP_STAMP_DIR)
-    list(APPEND file_deps ${dep_stamp_dir}${cfgdir}/${dep}-done)
+    _ep_get_step_stampfile(${dep} "done" done_stamp_file)
+    list(APPEND file_deps ${done_stamp_file})
   endforeach()
 
   get_property(cmd_set TARGET ${name} PROPERTY _EP_CONFIGURE_COMMAND SET)
@@ -1447,11 +1488,14 @@ function(ExternalProject_Add name)
 
   # Add a custom target for the external project.
   set(cmf_dir ${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles)
-  add_custom_target(${name} ALL DEPENDS ${cmf_dir}${cfgdir}/${name}-complete)
+  set(complete_stamp_file "${cmf_dir}${cfgdir}/${name}-complete")
+
+  add_custom_target(${name} ALL DEPENDS ${complete_stamp_file})
   set_property(TARGET ${name} PROPERTY _EP_IS_EXTERNAL_PROJECT 1)
   _ep_parse_arguments(ExternalProject_Add ${name} _EP_ "${ARGN}")
   _ep_set_directories(${name})
-  ExternalProject_Get_Property(${name} stamp_dir)
+  _ep_get_step_stampfile(${name} "done" done_stamp_file)
+  _ep_get_step_stampfile(${name} "install" install_stamp_file)
 
   # The 'complete' step depends on all other steps and creates a
   # 'done' mark.  A dependent external project's 'configure' step
@@ -1462,19 +1506,18 @@ function(ExternalProject_Add name)
   # parallel builds.  However, the Ninja generator needs to see the entire
   # dependency graph, and can cope with custom commands belonging to
   # multiple targets, so we add the 'done' mark as an output for Ninja only.
-  set(complete_outputs ${cmf_dir}${cfgdir}/${name}-complete)
+  set(complete_outputs ${complete_stamp_file})
   if(${CMAKE_GENERATOR} MATCHES "Ninja")
-    set(complete_outputs
-        ${complete_outputs} ${stamp_dir}${cfgdir}/${name}-done)
+    set(complete_outputs ${complete_outputs} ${done_stamp_file})
   endif()
 
   add_custom_command(
     OUTPUT ${complete_outputs}
     COMMENT "Completed '${name}'"
     COMMAND ${CMAKE_COMMAND} -E make_directory ${cmf_dir}${cfgdir}
-    COMMAND ${CMAKE_COMMAND} -E touch ${cmf_dir}${cfgdir}/${name}-complete
-    COMMAND ${CMAKE_COMMAND} -E touch ${stamp_dir}${cfgdir}/${name}-done
-    DEPENDS ${stamp_dir}${cfgdir}/${name}-install
+    COMMAND ${CMAKE_COMMAND} -E touch ${complete_stamp_file}
+    COMMAND ${CMAKE_COMMAND} -E touch ${done_stamp_file}
+    DEPENDS ${install_stamp_file}
     VERBATIM
     )