diff --git a/README.md b/README.md
index efde0c8..df70010 100644
--- a/README.md
+++ b/README.md
@@ -11,12 +11,16 @@ images tied to email or OpenID addresses.
 * Default avatar for unknown addresses
 * MD5 hashes
 * SHA256 hashes
-* Variable image size (`s`)
+* Variable image size (`s` or `size`)
+
+The default behaviour for unknown users is to return a 404 error. If a default
+image is put in the avatar directory, that is returned instead. This can not be
+overriden by adding the parameter `d=404` to the URL.
 
 ### Not supported
 
 * Avatar delivery based on OpenID
-* Default URL for missing images (`d`)
+* Default URL for missing images (`d` or `default`)
 
 ## Usage