diff --git a/lib/expand.ml b/lib/expand.ml
index bdb65d1..ddfe51b 100644
--- a/lib/expand.ml
+++ b/lib/expand.ml
@@ -283,12 +283,11 @@ let split_amp (items : Form.t list) : Form.t list * (string * Loc.t) option =
   in
   go [] items
 
+(* Never handed a [&]: every list of items reaching here has been through
+   [split_amp], which stops at the first one and refuses every way of getting
+   the tail wrong itself. So there is no arm for it and no sentence about it. *)
 let rec pat_of (f : Form.t) : pat =
   match f.Form.v with
-  | Form.Sym "&" ->
-    (* Only reachable inside a [ ] that [split_amp] already walked, so a second
-       [&] is the one that has no name of its own to go with. *)
-    Loc.fail f.Form.loc "& appears twice in this parameter list"
   | Form.Sym s -> Pname (s, f.Form.loc)
   | Form.Vec items ->
     let elems, rest = split_amp items in