diff --git a/bytecomp/switch.ml b/bytecomp/switch.ml
index 90dfde2..24e6d1c 100644
--- a/bytecomp/switch.ml
+++ b/bytecomp/switch.ml
@@ -722,7 +722,7 @@ let comp_clusters ({cases=cases ; actions=actions} as s) =
 let make_switch  {cases=cases ; actions=actions} i j =
   let ll,_,_ = cases.(i)
   and _,hh,_ = cases.(j) in
-  let tbl = Array.make (hh-ll+1) 0
+  let tbl = Array.make (hh-ll+1) (-1)
   and t = Hashtbl.create 17
   and index = ref 0 in
   let get_index act =
@@ -742,7 +742,11 @@ let make_switch  {cases=cases ; actions=actions} i j =
       tbl.(kk) <- index
     done
   done ;
-  let acts = Array.make !index actions.(0) in
+  let dummy = lazy (incr index; !index - 1) in
+  for i = 0 to Array.length tbl - 1 do
+    if tbl.(i) < 0 then tbl.(i) <- Lazy.force dummy
+  done;
+  let acts = Array.make !index (Arg.make_const 42) in
   Hashtbl.iter
     (fun act i -> acts.(i) <- actions.(act))
     t ;