diff --git a/NEXT.md b/NEXT.md
index fafe3e1..c6c7453 100644
--- a/NEXT.md
+++ b/NEXT.md
@@ -271,7 +271,11 @@ type-checks the wrapper against the generated prototype. Trusted: that the
 signature is the function's real signature — no header is read, deliberately,
 so nothing can check either. A `_Static_assert` on `sizeof`/`offsetof` was
 considered and rejected as circular: both sides would come from the same field
-list.
+list. Padding is not a separate hazard: for every field type the generator
+admits — the machine integers, the two floats, `bool`, a pointer and a nested
+struct — LLVM's layout is C's, and `emit.ml` writes no datalayout, so clang
+applies the target's rules to both halves. Everything where they could diverge
+is refused at the field.
 
 **One thing got sharper and should be said plainly:** the prototype is now
 generated *from the declaration*, so a scalar's width carries ABI weight it did
diff --git a/lib/shim.ml b/lib/shim.ml
index dfe6c99..4c8b8a0 100644
--- a/lib/shim.ml
+++ b/lib/shim.ml
@@ -40,6 +40,14 @@
     typedef permutes with it. And clang type-checks the wrapper against the
     [extern] prototype, so the flattening cannot disagree with the prototype.
 
+    Padding is not a separate hazard, which is worth saying because it reads
+    like one. For every field type this generator admits — the machine
+    integers, the two floats, [bool], a pointer and a nested struct — LLVM's
+    struct layout is C's, and [emit.ml] writes no datalayout, so clang applies
+    the target's own rules to both halves and they land in the same place.
+    Everything where the two could diverge — a fixed array, a slice, an
+    [Option], a map, a union — is refused at the field, by name.
+
     Trusted: that the [defstruct] describes the library's real struct, and that
     the [declare-c] signature is the function's real signature. No library
     header is read — deliberately, so a build needs the shared library and not
@@ -520,7 +528,7 @@ let flan_wrapper (fn : Ast.fn) (s : shim) raw : Ast.decl_kind =
 
 (* ── Expansion ──────────────────────────────────────────────────────── *)
 
-let one env (fn : Ast.fn) csym loc =
+let one env ~taken (fn : Ast.fn) csym loc =
   let needed = ref [] in
   let sargs =
     List.map
@@ -559,7 +567,15 @@ let one env (fn : Ast.fn) csym loc =
   let decls =
     if needs_flan then
       let raw = raw_name fn.Ast.name in
-      [ Ast.Declare (flattened fn s raw, s.swrap); flan_wrapper fn s raw ]
+      (* The flattened declaration's name is made up, so it can collide with
+         one somebody wrote. Refused here, naming both, rather than arriving as
+         the checker's "declared twice" about a name not in the file. *)
+      if Hashtbl.mem taken raw then
+        fail loc
+          "the declare-c of %s needs the name %s for the declaration it \
+           generates, and %s is declared already — rename one of them"
+          fn.Ast.name raw raw
+      else [ Ast.Declare (flattened fn s raw, s.swrap); flan_wrapper fn s raw ]
     else [ Ast.Declare (flattened fn s fn.Ast.name, s.swrap) ]
   in
   (decls, s, !needed)
@@ -569,6 +585,16 @@ let one env (fn : Ast.fn) csym loc =
    no C compile. *)
 let expand (decls : Ast.decl list) : Ast.decl list * string option =
   let env = scan decls in
+  (* The flattened declaration's name is made up, so it can collide with one
+     somebody wrote. Refused here, naming both, rather than surfacing as the
+     checker's "declared twice" about a name that is not in the file. *)
+  let taken = Hashtbl.create 64 in
+  List.iter
+    (fun (d : Ast.decl) ->
+       match Ast.declared_name d with
+       | Some n -> Hashtbl.replace taken n d.Ast.dloc
+       | None -> ())
+    decls;
   let shims = ref [] in
   let needed = ref [] in
   let out =
@@ -576,7 +602,7 @@ let expand (decls : Ast.decl list) : Ast.decl list * string option =
       (fun (d : Ast.decl) ->
          match d.Ast.d with
          | Ast.DeclareC (fn, csym) ->
-           let ds, s, n = one env fn csym d.Ast.dloc in
+           let ds, s, n = one env ~taken fn csym d.Ast.dloc in
            shims := !shims @ [ s ];
            List.iter
              (fun x -> if not (List.mem x !needed) then needed := !needed @ [ x ])
diff --git a/test/test_acceptance.ml b/test/test_acceptance.ml
index cb3f018..04b5ed8 100644
--- a/test/test_acceptance.ml
+++ b/test/test_acceptance.ml
@@ -680,6 +680,11 @@ let () =
     shim_refuses "declare-c: a field C cannot hold"
       "(defstruct S [xs [i32]])\n(declare-c f [s S] \"F\")"
       "field xs of S is a slice";
+    shim_refuses "declare-c: the generated name is already taken"
+      (v2
+       ^ "(defn mid-c [a (Ptr Vector2)  out (Ptr Vector2)])\n\
+          (declare-c mid [a Vector2] Vector2 \"Mid\")")
+      "needs the name mid-c for the declaration it generates";
     shim_refuses "declare-c: two Flan names for one C function"
       "(declare-c a [] \"Same\")\n(declare-c b [] \"Same\")"
       "one declare-c per C function";
diff --git a/vendor/raylib/raylib.flan b/vendor/raylib/raylib.flan
index a84dc2b..a2d4d9a 100644
--- a/vendor/raylib/raylib.flan
+++ b/vendor/raylib/raylib.flan
@@ -391,7 +391,7 @@
   [center Vector2  radius f32  color Color]
   "DrawCircleLinesV")
 
-;; Two radii, horizontal then vertical. Equal radii is a circle, so a wrapper
+;; Two radii, horizontal then vertical. Equal radii is a circle, so a binding
 ;; that exchanged them would be invisible unless they differ — which is why
 ;; sand.flan's ellipse is deliberately wider than it is tall.
 (declare-c draw-ellipse