diff --git a/src/Composer/Command/InstallCommand.php b/src/Composer/Command/InstallCommand.php
index c578a308c..7bcda88ab 100644
--- a/src/Composer/Command/InstallCommand.php
+++ b/src/Composer/Command/InstallCommand.php
@@ -64,7 +64,7 @@ EOT
         $install
             ->setDryRun($input->getOption('dry-run'))
             ->setVerbose($input->getOption('verbose'))
-            ->setPreferSource($input->getOption('prefer-source'))
+            ->setPreferSource($input->getOption('prefer-source') || $composer->getConfig()->get('prefer-source'))
             ->setPreferDist($input->getOption('prefer-dist'))
             ->setDevMode($input->getOption('dev'))
             ->setRunScripts(!$input->getOption('no-scripts'))
diff --git a/src/Composer/Command/UpdateCommand.php b/src/Composer/Command/UpdateCommand.php
index f1ac08f28..6515bbb83 100644
--- a/src/Composer/Command/UpdateCommand.php
+++ b/src/Composer/Command/UpdateCommand.php
@@ -67,7 +67,7 @@ EOT
         $install
             ->setDryRun($input->getOption('dry-run'))
             ->setVerbose($input->getOption('verbose'))
-            ->setPreferSource($input->getOption('prefer-source'))
+            ->setPreferSource($input->getOption('prefer-source') || $composer->getConfig()->get('prefer-source'))
             ->setPreferDist($input->getOption('prefer-dist'))
             ->setDevMode(!$input->getOption('no-dev'))
             ->setRunScripts(!$input->getOption('no-scripts'))