-With numeric arg, turn ERC fill mode on if and only if arg is
-positive. In ERC fill mode, messages in the channel buffers are
-filled."
+With a prefix argument ARG, enable ERC fill mode if ARG is
+positive, and disable it otherwise. If called from Lisp, enable
+the mode if ARG is omitted or nil.
+
+ERC fill mode is a global minor mode. When enabled, messages in
+the channel buffers are filled."