From b268e20d9fa9e9e4d058bc3ca7eff7ec5e5ff611 Mon Sep 17 00:00:00 2001
From: Jordi Boggiano <j.boggiano@seld.be>
Date: Tue, 4 May 2021 16:43:24 +0200
Subject: [PATCH] Fix invalid interface usage

---
 src/Composer/Command/UpdateCommand.php | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/Composer/Command/UpdateCommand.php b/src/Composer/Command/UpdateCommand.php
index 7386b915a..c5ce5cb68 100644
--- a/src/Composer/Command/UpdateCommand.php
+++ b/src/Composer/Command/UpdateCommand.php
@@ -17,6 +17,7 @@ use Composer\DependencyResolver\Request;
 use Composer\Installer;
 use Composer\IO\IOInterface;
 use Composer\Package\Loader\RootPackageLoader;
+use Composer\Package\RootPackage;
 use Composer\Plugin\CommandEvent;
 use Composer\Plugin\PluginEvents;
 use Composer\Package\Version\VersionParser;
@@ -154,7 +155,9 @@ EOT
         }
         $rootPackage->setRequires($rootRequires);
         $rootPackage->setDevRequires($rootDevRequires);
-        $rootPackage->setReferences(RootPackageLoader::extractReferences($reqs, $rootPackage->getReferences()));
+        if ($rootPackage instanceof RootPackage) {
+            $rootPackage->setReferences(RootPackageLoader::extractReferences($reqs, $rootPackage->getReferences()));
+        }
         $rootPackage->setStabilityFlags(RootPackageLoader::extractStabilityFlags($reqs, $rootPackage->getMinimumStability(), $rootPackage->getStabilityFlags()));
 
         if ($input->getOption('interactive')) {