diff --git a/cache/admin.php b/cache/admin.php
index f3e3acb120d..c9c35db6adb 100644
--- a/cache/admin.php
+++ b/cache/admin.php
@@ -282,6 +282,7 @@ if (!empty($action) && confirm_sesskey()) {
 
 $PAGE->set_title($title);
 $PAGE->set_heading($SITE->fullname);
+/* @var core_cache_renderer $renderer */
 $renderer = $PAGE->get_renderer('core_cache');
 
 echo $renderer->header();
diff --git a/cache/classes/helper.php b/cache/classes/helper.php
index 970cbd500e5..0d0529ebc64 100644
--- a/cache/classes/helper.php
+++ b/cache/classes/helper.php
@@ -678,4 +678,28 @@ class cache_helper {
             }
         }
     }
+
+    /**
+     * Returns an array of stores that would meet the requirements for every definition.
+     *
+     * These stores would be 100% suitable to map as defaults for cache modes.
+     *
+     * @return array[] An array of stores, keys are the store names.
+     */
+    public static function get_stores_suitable_for_mode_default() {
+        $factory = cache_factory::instance();
+        $config = $factory->create_config_instance();
+        $requirements = 0;
+        foreach ($config->get_definitions() as $definition) {
+            $definition = cache_definition::load($definition['component'].'/'.$definition['area'], $definition);
+            $requirements = $requirements | $definition->get_requirements_bin();
+        }
+        $stores = array();
+        foreach ($config->get_all_stores() as $name => $store) {
+            if (!empty($store['features']) && ($store['features'] & $requirements)) {
+                $stores[$name] = $store;
+            }
+        }
+        return $stores;
+    }
 }
diff --git a/cache/locallib.php b/cache/locallib.php
index c72c52c5e87..2d83b9447cb 100644
--- a/cache/locallib.php
+++ b/cache/locallib.php
@@ -1126,7 +1126,10 @@ abstract class cache_administration_helper extends cache_helper {
      * @return array An array containing sub-arrays, one for each mode.
      */
     public static function get_default_mode_stores() {
+        global $OUTPUT;
         $instance = cache_config::instance();
+        $adequatestores = cache_helper::get_stores_suitable_for_mode_default();
+        $icon = new pix_icon('i/warning', new lang_string('inadequatestoreformapping', 'cache'));
         $storenames = array();
         foreach ($instance->get_all_stores() as $key => $store) {
             if (!empty($store['default'])) {
@@ -1149,6 +1152,9 @@ abstract class cache_administration_helper extends cache_helper {
             } else {
                 $modemappings[$mode][$mapping['store']] = $mapping['store'];
             }
+            if (!array_key_exists($mapping['store'], $adequatestores)) {
+                $modemappings[$mode][$mapping['store']] = $modemappings[$mode][$mapping['store']].' '.$OUTPUT->render($icon);
+            }
         }
         return $modemappings;
     }
diff --git a/lang/en/cache.php b/lang/en/cache.php
index 461edde1acf..6d4eab72f76 100644
--- a/lang/en/cache.php
+++ b/lang/en/cache.php
@@ -92,6 +92,7 @@ $string['ex_unabletolock'] = 'Unable to acquire a lock for caching.';
 $string['ex_unmetstorerequirements'] = 'You are unable to use this store at the present time. Please refer to the documentation to determine its requirements.';
 $string['gethit'] = 'Get - Hit';
 $string['getmiss'] = 'Get - Miss';
+$string['inadequatestoreformapping'] = 'This store doesn\'t meet the requirements for all known definitions. Definitions for which this store is inadequate will be given the original default store instead of the selected store.';
 $string['invalidlock'] = 'Invalid lock';
 $string['invalidplugin'] = 'Invalid plugin';
 $string['invalidstore'] = 'Invalid cache store provided';