===================================================================
--- typing/cmt_format.ml	(revision 50428)
+++ typing/cmt_format.ml	(working copy)
@@ -76,17 +76,19 @@
   try ignore (Sys.getenv "OCAML_BINANNOT_WITHENV"); false
   with Not_found -> true
 
-(* Re-introduce sharing after clearing environments *)
+let last_env = ref None
+
 let env_hcons = Hashtbl.create 133
 let keep_only_summary env =
-  let new_env = Env.keep_only_summary env in
-  try
-    Hashtbl.find env_hcons new_env
-  with Not_found ->
-    Hashtbl.add env_hcons new_env new_env;
-    new_env
-let clear_env_hcons () = Hashtbl.clear env_hcons
+  match !last_env with
+  | Some (e0, e1) when e0 == env -> e1
+  | _ ->
+      let new_env = Env.keep_only_summary env in
+      last_env := Some (env, new_env);
+      new_env
 
+let clear_env_hcons () = last_env := None
+
 module ClearEnv  = TypedtreeMap.MakeMap (struct
   open TypedtreeMap
   include DefaultMapArgument
===================================================================