diff --git a/blocks/moodleblock.class.php b/blocks/moodleblock.class.php
index 333893d27c5..c78b68a3d89 100644
--- a/blocks/moodleblock.class.php
+++ b/blocks/moodleblock.class.php
@@ -343,10 +343,12 @@ class block_base {
      * Default behavior: save all variables as $CFG properties
      * You don't need to override this if you 're satisfied with the above
      *
+     * @deprecated since Moodle 2.9 MDL-49385 - Please use Admin Settings functionality to save block configuration.
      * @param array $data
      * @return boolean
      */
     function config_save($data) {
+        debugging('config_save($data) is deprecated, use Admin Settings functionality to save block configuration.', DEBUG_DEVELOPER);
         foreach ($data as $name => $value) {
             set_config($name, $value);
         }
diff --git a/blocks/upgrade.txt b/blocks/upgrade.txt
index 288eff356eb..573aaeb5e46 100644
--- a/blocks/upgrade.txt
+++ b/blocks/upgrade.txt
@@ -4,6 +4,7 @@ information provided here is intended especially for developers.
 === 2.9 ===
 
 * The obsolete method preferred_width() was removed (it was not doing anything)
+* Deprecated block_base::config_save as is not called anywhere and should not be used.
 
 === 2.8 ===