diff --git a/lib/ast.ml b/lib/ast.ml
index 1251524..2edcf93 100644
--- a/lib/ast.ml
+++ b/lib/ast.ml
@@ -16,7 +16,7 @@ and texpr_kind =
   | Tname  of string                  (* i32  bool  Cursor  string *)
   | Tslice of texpr                   (* [u8]                      ptr+len *)
   | Tarray of len * texpr             (* [4 f32]  [rows [cols u32]]        *)
-  | Tmap   of texpr * texpr           (* {string i32}                      *)
+  | Tmap   of texpr * texpr           (* (Map string i32)                  *)
   | Tapp   of string * texpr list     (* (Ptr Cursor)  (Option f64)        *)
   | Tfn    of texpr list * texpr      (* (Fn [a a] bool)                   *)
 
diff --git a/lib/form.ml b/lib/form.ml
index 121ee07..b16ace0 100644
--- a/lib/form.ml
+++ b/lib/form.ml
@@ -17,7 +17,9 @@ and value =
   | Byte  of int           (* \space  \0  \(                   (0..255) *)
   | List  of t list        (* (f x) *)
   | Vec   of t list        (* [1 2 3]  and every binding/type bracket *)
-  | Map   of t list        (* {.field v} a struct value, {K V} a type. The
+  | Map   of t list        (* {.field v} a struct value, and a defn's
+                              {:where ...} clause. Braces are not a type: the
+                              {K V} spelling was withdrawn for (Map K V). The
                               colon spelling is left for map literals. *)
 
 let make v loc = { v; loc }
diff --git a/lib/types.ml b/lib/types.ml
index ee7f714..90f700f 100644
--- a/lib/types.ml
+++ b/lib/types.ml
@@ -28,7 +28,7 @@ type t =
   | Enum   of string
   | Slice  of t                       (* [T]     ptr+len, non-owning *)
   | Array  of int64 * t               (* [n T]   inline, a value, copies *)
-  | Map    of t * t                   (* {K V} *)
+  | Map    of t * t                   (* (Map K V) *)
   | Ptr    of t                       (* (Ptr T) *)
   (* [Allocator]: a builtin opaque type, the way [string] is a builtin
      ptr+len. It is a [Types.t] case with no user-writable constructor, which