diff --git a/lib/runtime/code.ml b/lib/runtime/code.ml
index c02350a..7192e6d 100644
--- a/lib/runtime/code.ml
+++ b/lib/runtime/code.ml
@@ -25,7 +25,7 @@ type ins =
   | CON of reg * vtable
   | CAL of reg * reg * reg * reg list
   (* control flow *)
-  | RET
+  | RET of reg
   | JMP of block
   | CBR of reg * block * block
 
@@ -58,7 +58,7 @@ let frame_size t =
   in
   let meas (R i) fs = max fs (i + 1) in
   let meas_ins fs = function
-    | RET -> fs
+    | RET r
     | LDI (r, _)
     | CON (r, _)
       -> meas r fs
@@ -128,7 +128,7 @@ let pp_ins ~label ppf = function
     Fmt.pf ppf "cal %a, %a[%a](" pp_reg a pp_reg b pp_reg c;
     List.iteri (fun i d -> if i > 0 then Fmt.pf ppf ","; pp_reg ppf d) ds;
     Fmt.pf ppf ")"
-  | RET -> Fmt.pf ppf "ret"
+  | RET a -> Fmt.pf ppf "ret %a" pp_reg a
   | JMP b -> Fmt.pf ppf "jmp %s" (label b)
   | CBR (a, b1, b2) ->
     let l1 = label b1 in
diff --git a/lib/runtime/interp.ml b/lib/runtime/interp.ml
index 8b6ab58..781cf75 100644
--- a/lib/runtime/interp.ml
+++ b/lib/runtime/interp.ml
@@ -60,6 +60,7 @@ end
 type frame = {
   r : Value.t array;
   mutable pc : Code.ins list;
+  mutable rv : Value.t;
 }
 
 let jmp fr b = fr.pc <- Code.instructions b
@@ -85,7 +86,8 @@ let rec exec ({ r; _ } as fr) = function
   | Code.JMP b -> jmp fr b
   | Code.CBR (R a, b1, b2) ->
     jmp fr (if Value.truthy r.(a) then b1 else b2)
-  | Code.RET ->
+  | Code.RET (R a) ->
+    fr.rv <- r.(a);
     fr.pc <- []
 
 and call mthd self args =
@@ -108,9 +110,9 @@ and step fr =
 
 and run prog self (* args *) =
   let r = Array.make (Code.frame_size prog) Value.Nil in
-  let fr = { r; pc = [] } in
+  let fr = { r; pc = []; rv = Nil } in
   r.(0) <- self;
   jmp fr prog.entry;
   step fr;
-  r.(0)
+  fr.rv