diff --git a/lisp/yank-media.el b/lisp/yank-media.el
index cafc198be85..66eb23430ec 100644
--- a/lisp/yank-media.el
+++ b/lisp/yank-media.el
@@ -91,7 +91,11 @@ the `register-yank-media-handler' mechanism."
 (defun register-yank-media-handler (types handler)
   "Register HANDLER for dealing with `yank-media' actions for TYPES.
 TYPES should be a MIME media type symbol, a regexp, or a list
-that can contain both symbols and regexps."
+that can contain both symbols and regexps.
+
+HANDLER is a function that will be called with two arguments: The
+MIME type (a symbol on the form `image/png') and the selection
+data (a string)."
   (make-local-variable 'yank-media--registered-handlers)
   (dolist (type (ensure-list types))
     (setf (alist-get type yank-media--registered-handlers nil nil #'equal)