diff --git a/README.md b/README.md
index 56e97de..ce2fb8d 100644
--- a/README.md
+++ b/README.md
@@ -55,7 +55,9 @@ libravatarserv looks in each of `${XDG_DATA_DIRS}` for a directory named
 variable `LIBRAVATARSERV_DIR` (until 0.3.0 `AVATAR_DIR`).
 
 The image files are named like your email address, no file extension. If you
-want to deliver a default image for unknown email addresses, name it `default`.
+want to force a default image for unknown email addresses, name it `default`.
+The default image overrides the specified fallback in the URL and in the
+environment variable.
 
 If you want to support "Mystery persons" (mp/mm) as default avatars, place a
 file named `mp` in the avatar dir. You can use the [default libravatar mystery