diff --git a/lib/classes/plugin_manager.php b/lib/classes/plugin_manager.php
index aa170a1ae5d..dfd5943b586 100644
--- a/lib/classes/plugin_manager.php
+++ b/lib/classes/plugin_manager.php
@@ -591,19 +591,12 @@ class core_plugin_manager {
      * @return string
      */
     public function plugintype_name($type) {
-
         if (get_string_manager()->string_exists('type_' . $type, 'core_plugin')) {
             // For most plugin types, their names are defined in core_plugin lang file.
             return get_string('type_' . $type, 'core_plugin');
-
         } else if ($parent = $this->get_parent_of_subplugin($type)) {
             // If this is a subplugin, try to ask the parent plugin for the name.
-            if (get_string_manager()->string_exists('subplugintype_' . $type, $parent)) {
-                return $this->plugin_name($parent) . ' / ' . get_string('subplugintype_' . $type, $parent);
-            } else {
-                return $this->plugin_name($parent) . ' / ' . $type;
-            }
-
+            return $this->plugin_name($parent) . ' / ' . get_string('subplugintype_' . $type, $parent);
         } else {
             return $type;
         }
@@ -620,19 +613,12 @@ class core_plugin_manager {
      * @return string
      */
     public function plugintype_name_plural($type) {
-
         if (get_string_manager()->string_exists('type_' . $type . '_plural', 'core_plugin')) {
             // For most plugin types, their names are defined in core_plugin lang file.
             return get_string('type_' . $type . '_plural', 'core_plugin');
-
         } else if ($parent = $this->get_parent_of_subplugin($type)) {
             // If this is a subplugin, try to ask the parent plugin for the name.
-            if (get_string_manager()->string_exists('subplugintype_' . $type . '_plural', $parent)) {
-                return $this->plugin_name($parent) . ' / ' . get_string('subplugintype_' . $type . '_plural', $parent);
-            } else {
-                return $this->plugin_name($parent) . ' / ' . $type;
-            }
-
+            return $this->plugin_name($parent) . ' / ' . get_string('subplugintype_' . $type . '_plural', $parent);
         } else {
             return $type;
         }
diff --git a/lib/upgrade.txt b/lib/upgrade.txt
index abbbf7d2aec..8f029d70c6f 100644
--- a/lib/upgrade.txt
+++ b/lib/upgrade.txt
@@ -15,6 +15,8 @@ information provided here is intended especially for developers.
   drag/drop, which can be used to add transition effects in calling code
 * course_modinfo now has a purge_course_modules_cache() method, which takes a list of cmids and purges
   them all in a single cache set.
+* The `core_plugin_manager::plugintype_name[_plural]` methods now require language strings for subplugin types always
+  be defined in plugins (via `subplugintype_<type>` and `subplugintype_<type>_plural` language strings)
 * Behat generators can now implement the function finish_generate_ to detect when the whole list of elements have been generated.
 * New return value 'icon' has been added to the 'external_files' webservice structure. This return value represents the
   relative path to the relevant file type icon based on the file's mime type.