diff --git a/src/Composer/Repository/Vcs/VcsDriver.php b/src/Composer/Repository/Vcs/VcsDriver.php
index 37946da23..f174f8527 100644
--- a/src/Composer/Repository/Vcs/VcsDriver.php
+++ b/src/Composer/Repository/Vcs/VcsDriver.php
@@ -81,7 +81,7 @@ abstract class VcsDriver implements VcsDriverInterface
      */
     protected function shouldCache($identifier)
     {
-        return $this->cache && preg_match('{[a-f0-9]{40}}i', $identifier);
+        return $this->cache && preg_match('{^[a-f0-9]{40}$}iD', $identifier);
     }
 
     /**