diff --git a/src/Composer/Factory.php b/src/Composer/Factory.php
index de1516f7d..9a7da447d 100644
--- a/src/Composer/Factory.php
+++ b/src/Composer/Factory.php
@@ -414,7 +414,7 @@ class Factory
             $locker = new Package\Locker($io, new JsonFile($config->get('lock') ? $lockFile : Platform::getDevNull(), null, $io), $im, file_get_contents($composerFile), $process);
             $composer->setLocker($locker);
         } elseif ($composer instanceof Composer) {
-            $locker = new Package\Locker($io, new JsonFile(Platform::getDevNull(), null, $io), $im, json_encode($localConfig), $process);
+            $locker = new Package\Locker($io, new JsonFile(Platform::getDevNull(), null, $io), $im, JsonFile::encode($localConfig), $process);
             $composer->setLocker($locker);
         }