diff --git a/UPGRADE_TO_2_3 b/UPGRADE_TO_2_3
index 39b0d1f9d..10e8a41f4 100644
--- a/UPGRADE_TO_2_3
+++ b/UPGRADE_TO_2_3
@@ -30,3 +30,11 @@ Also, related functions were affected:
 
 Internal changes were made to DQL and SQL generation. If you have implemented your own TreeWalker,
 you probably need to update it. The method walkJoinVariableDeclaration is now named walkJoin.
+
+# Metadata Drivers
+
+Metadata drivers have been rewritten to reuse code from Doctrine\Common.
+Anyone who is using the `Doctrine\ORM\Mapping\Driver\Driver` interface
+explicitly should instead refer to `Doctrine\Common\Persistence\Mapping\Driver\MappingDriver`.
+Same applies to `Doctrine\ORM\Mapping\Driver\AbstractFileDriver`: you should now refer to
+`Doctrine\Common\Persistence\Mapping\Driver\FileDriver`.
\ No newline at end of file