diff --git a/includes/Hooks.php b/includes/Hooks.php
index c4a56f671..011a0d0e0 100644
--- a/includes/Hooks.php
+++ b/includes/Hooks.php
@@ -1417,6 +1417,11 @@ class Hooks implements
 			// option changes. This covers both explicit changes in the preferences
 			// and changes made through the options API (since both call this hook).
 			DeferredUpdates::addCallableUpdate( static function () use ( $user ) {
+				if ( !$user->isRegistered() ) {
+					// It's possible the user account was deleted before the deferred
+					// update runs (T318081)
+					return;
+				}
 				MWEchoNotifUser::newFromUser( $user )->resetNotificationCount();
 			} );
 		}