diff --git a/lib/pluginlib.php b/lib/pluginlib.php
index 5347b1615ca..9d788a765ed 100644
--- a/lib/pluginlib.php
+++ b/lib/pluginlib.php
@@ -1461,7 +1461,7 @@ class plugintype_auth extends plugintype_base implements plugin_information {
         }
 
         if (is_null($enabled)) {
-            $enabled = explode(',', $CFG->auth);
+            $enabled = array_flip(explode(',', $CFG->auth));
         }
 
         return isset($enabled[$this->name]);
@@ -1498,7 +1498,7 @@ class plugintype_enrol extends plugintype_base implements plugin_information {
         static $enabled = null;
 
         if (is_null($enabled)) {
-            $enabled = explode(',', $CFG->enrol_plugins_enabled);
+            $enabled = array_flip(explode(',', $CFG->enrol_plugins_enabled));
         }
 
         return isset($enabled[$this->name]);