diff --git a/auth/cas/auth.php b/auth/cas/auth.php
index 8e137eb1a4b..fb42870df0b 100644
--- a/auth/cas/auth.php
+++ b/auth/cas/auth.php
@@ -500,6 +500,7 @@ if ( !is_object($PHPCAS_CLIENT) ) {
                 }
             }
         }
+        $moodleattributes['username'] = $this->config->user_attribute;
         return $moodleattributes;
     }
     /**
diff --git a/auth/db/auth.php b/auth/db/auth.php
index ba3cf7529f7..c0f57aff6fa 100644
--- a/auth/db/auth.php
+++ b/auth/db/auth.php
@@ -137,6 +137,7 @@ class auth_plugin_db extends auth_plugin_base {
                 $moodleattributes[$field] = $this->config->{"field_map_$field"};
             }
         }
+        $moodleattributes['username'] = $this->config->fielduser;
         return $moodleattributes;
     }
 
diff --git a/auth/ldap/auth.php b/auth/ldap/auth.php
index e3902a72d5c..d7eeea7e49a 100644
--- a/auth/ldap/auth.php
+++ b/auth/ldap/auth.php
@@ -1637,6 +1637,7 @@ class auth_plugin_ldap extends auth_plugin_base {
                 }
             }
         }
+        $moodleattributes['username'] = $this->config->user_attribute;
         return $moodleattributes;
     }
 
diff --git a/auth/shibboleth/auth.php b/auth/shibboleth/auth.php
index 84309c28a9c..8ed938150fe 100644
--- a/auth/shibboleth/auth.php
+++ b/auth/shibboleth/auth.php
@@ -128,6 +128,7 @@ class auth_plugin_shibboleth extends auth_plugin_base {
                 $moodleattributes[$field] = $configarray["field_map_$field"];
             }
         }
+        $moodleattributes['username'] = $configarray["user_attribute"];
 
         return $moodleattributes;
     }
diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index 14ba40c7736..b8ac39df34a 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -2831,6 +2831,10 @@ function update_user_record($username, $authplugin) {
     if ($newinfo = $userauth->get_userinfo($username)) {
         $newinfo = truncate_userinfo($newinfo);
         foreach ($newinfo as $key => $value){
+            if ($key === 'username') {
+                // 'username' is not a mapped updateable/lockable field, so skip it.
+                continue;
+            }
             $confval = $userauth->config->{'field_updatelocal_' . $key};
             $lockval = $userauth->config->{'field_lock_' . $key};
             if (empty($confval) || empty($lockval)) {