diff --git a/stdlib/hashtbl.ml b/stdlib/hashtbl.ml
index 955f63845..401b5992f 100644
--- a/stdlib/hashtbl.ml
+++ b/stdlib/hashtbl.ml
@@ -36,7 +36,7 @@ type ('a, 'b) t =
 
 and ('a, 'b) bucketlist =
     Empty
-  | Cons of 'a * 'b * ('a, 'b) bucketlist
+  | Cons of { key: 'a; data: 'b; rest: ('a, 'b) bucketlist }
 
 (* To pick random seeds if requested *)
 
@@ -95,10 +95,10 @@ let resize indexfun h =
     h.data <- ndata;          (* so that indexfun sees the new bucket count *)
     let rec insert_bucket = function
         Empty -> ()
-      | Cons(key, data, rest) ->
+      | Cons{key; data; rest} ->
           insert_bucket rest; (* preserve original order of elements *)
           let nidx = indexfun h key in
-          ndata.(nidx) <- Cons(key, data, ndata.(nidx)) in
+          ndata.(nidx) <- Cons{key; data; rest=ndata.(nidx)} in
     for i = 0 to osize - 1 do
       insert_bucket odata.(i)
     done
@@ -112,7 +112,7 @@ let key_index h key =
 
 let add h key info =
   let i = key_index h key in
-  let bucket = Cons(key, info, h.data.(i)) in
+  let bucket = Cons{key; data=info; rest=h.data.(i)} in
   h.data.(i) <- bucket;
   h.size <- h.size + 1;
   if h.size > Array.length h.data lsl 1 then resize key_index h
@@ -121,38 +121,38 @@ let remove h key =
   let rec remove_bucket = function
     | Empty ->
         Empty
-    | Cons(k, i, next) ->
+    | Cons{key=k; data=i; rest=next} ->
         if compare k key = 0
         then begin h.size <- h.size - 1; next end
-        else Cons(k, i, remove_bucket next) in
+        else Cons{key=k; data=i; rest=remove_bucket next} in
   let i = key_index h key in
   h.data.(i) <- remove_bucket h.data.(i)
 
 let rec find_rec key = function
   | Empty ->
       raise Not_found
-  | Cons(k, d, rest) ->
+  | Cons{key=k; data=d; rest} ->
       if compare key k = 0 then d else find_rec key rest
 
 let find h key =
   match h.data.(key_index h key) with
   | Empty -> raise Not_found
-  | Cons(k1, d1, rest1) ->
+  | Cons{key=k1; data=d1; rest=rest1} ->
       if compare key k1 = 0 then d1 else
       match rest1 with
       | Empty -> raise Not_found
-      | Cons(k2, d2, rest2) ->
+      | Cons{key=k2; data=d2; rest=rest2} ->
           if compare key k2 = 0 then d2 else
           match rest2 with
           | Empty -> raise Not_found
-          | Cons(k3, d3, rest3) ->
+          | Cons{key=k3; data=d3; rest=rest3} ->
               if compare key k3 = 0 then d3 else find_rec key rest3
 
 let find_all h key =
   let rec find_in_bucket = function
   | Empty ->
       []
-  | Cons(k, d, rest) ->
+  | Cons{key=k; data=d; rest} ->
       if compare k key = 0
       then d :: find_in_bucket rest
       else find_in_bucket rest in
@@ -162,16 +162,16 @@ let replace h key info =
   let rec replace_bucket = function
     | Empty ->
         raise_notrace Not_found
-    | Cons(k, i, next) ->
+    | Cons{key=k; data=i; rest=next} ->
         if compare k key = 0
-        then Cons(key, info, next)
-        else Cons(k, i, replace_bucket next) in
+        then Cons{key; data=info; rest=next}
+        else Cons{key=k; data=i; rest=replace_bucket next} in
   let i = key_index h key in
   let l = h.data.(i) in
   try
     h.data.(i) <- replace_bucket l
   with Not_found ->
-    h.data.(i) <- Cons(key, info, l);
+    h.data.(i) <- Cons{key; data=info; rest=l};
     h.size <- h.size + 1;
     if h.size > Array.length h.data lsl 1 then resize key_index h
 
@@ -179,7 +179,7 @@ let mem h key =
   let rec mem_in_bucket = function
   | Empty ->
       false
-  | Cons(k, d, rest) ->
+  | Cons{key=k; data=d; rest} ->
       compare k key = 0 || mem_in_bucket rest in
   mem_in_bucket h.data.(key_index h key)
 
@@ -187,7 +187,7 @@ let iter f h =
   let rec do_bucket = function
     | Empty ->
         ()
-    | Cons(k, d, rest) ->
+    | Cons{key=k; data=d; rest} ->
         f k d; do_bucket rest in
   let d = h.data in
   for i = 0 to Array.length d - 1 do
@@ -213,7 +213,7 @@ let fold f h init =
     match b with
       Empty ->
         accu
-    | Cons(k, d, rest) ->
+    | Cons{key=k; data=d; rest} ->
         do_bucket rest (f k d accu) in
   let d = h.data in
   let accu = ref init in
@@ -231,7 +231,7 @@ type statistics = {
 
 let rec bucket_length accu = function
   | Empty -> accu
-  | Cons(_, _, rest) -> bucket_length (accu + 1) rest
+  | Cons{rest} -> bucket_length (accu + 1) rest
 
 let stats h =
   let mbl =
@@ -320,7 +320,7 @@ module MakeSeeded(H: SeededHashedType): (SeededS with type key = H.t) =
 
     let add h key info =
       let i = key_index h key in
-      let bucket = Cons(key, info, h.data.(i)) in
+      let bucket = Cons{key; data=info; rest=h.data.(i)} in
       h.data.(i) <- bucket;
       h.size <- h.size + 1;
       if h.size > Array.length h.data lsl 1 then resize key_index h
@@ -329,38 +329,38 @@ module MakeSeeded(H: SeededHashedType): (SeededS with type key = H.t) =
       let rec remove_bucket = function
         | Empty ->
             Empty
-        | Cons(k, i, next) ->
+        | Cons{key=k; data=i; rest=next} ->
             if H.equal k key
             then begin h.size <- h.size - 1; next end
-            else Cons(k, i, remove_bucket next) in
+            else Cons{key=k; data=i; rest=remove_bucket next} in
       let i = key_index h key in
       h.data.(i) <- remove_bucket h.data.(i)
 
     let rec find_rec key = function
       | Empty ->
           raise Not_found
-      | Cons(k, d, rest) ->
+      | Cons{key=k; data=d; rest} ->
           if H.equal key k then d else find_rec key rest
 
     let find h key =
       match h.data.(key_index h key) with
       | Empty -> raise Not_found
-      | Cons(k1, d1, rest1) ->
+      | Cons{key=k1; data=d1; rest=rest1} ->
           if H.equal key k1 then d1 else
           match rest1 with
           | Empty -> raise Not_found
-          | Cons(k2, d2, rest2) ->
+          | Cons{key=k2; data=d2; rest=rest2} ->
               if H.equal key k2 then d2 else
               match rest2 with
               | Empty -> raise Not_found
-              | Cons(k3, d3, rest3) ->
+              | Cons{key=k3; data=d3; rest=rest3} ->
                   if H.equal key k3 then d3 else find_rec key rest3
 
     let find_all h key =
       let rec find_in_bucket = function
       | Empty ->
           []
-      | Cons(k, d, rest) ->
+      | Cons{key=k; data=d; rest} ->
           if H.equal k key
           then d :: find_in_bucket rest
           else find_in_bucket rest in
@@ -370,16 +370,16 @@ module MakeSeeded(H: SeededHashedType): (SeededS with type key = H.t) =
       let rec replace_bucket = function
         | Empty ->
             raise_notrace Not_found
-        | Cons(k, i, next) ->
+        | Cons{key=k; data=i; rest=next} ->
             if H.equal k key
-            then Cons(key, info, next)
-            else Cons(k, i, replace_bucket next) in
+            then Cons{key; data=info; rest=next}
+            else Cons{key = k; data=i; rest=replace_bucket next} in
       let i = key_index h key in
       let l = h.data.(i) in
       try
         h.data.(i) <- replace_bucket l
       with Not_found ->
-        h.data.(i) <- Cons(key, info, l);
+        h.data.(i) <- Cons{key; data=info; rest=l};
         h.size <- h.size + 1;
         if h.size > Array.length h.data lsl 1 then resize key_index h
 
@@ -387,7 +387,7 @@ module MakeSeeded(H: SeededHashedType): (SeededS with type key = H.t) =
       let rec mem_in_bucket = function
       | Empty ->
           false
-      | Cons(k, d, rest) ->
+      | Cons{key=k; data=d; rest} ->
           H.equal k key || mem_in_bucket rest in
       mem_in_bucket h.data.(key_index h key)