diff --git camlp4/Camlp4/Struct/Grammar/Delete.ml camlp4/Camlp4/Struct/Grammar/Delete.ml
index 929ac2b..4e3ce5a 100644
--- camlp4/Camlp4/Struct/Grammar/Delete.ml
+++ camlp4/Camlp4/Struct/Grammar/Delete.ml
@@ -17,9 +17,12 @@
  * - Nicolas Pouillard: refactoring
  *)
 
+exception Rule_not_found of string;
+
 module Make (Structure : Structure.S) = struct
   module Tools  = Tools.Make Structure;
   module Parser = Parser.Make Structure;
+  module Print = Print.Make Structure;
   open Structure;
 
 (* Deleting a rule *)
@@ -83,6 +86,17 @@ and decr_keyw_use_in_tree gram =
         decr_keyw_use_in_tree gram n.brother
       } ]
 ;
+
+value rule_not_found _entry symbols =
+  let b = Buffer.create 13 in
+  let ppf = Format.formatter_of_buffer b in
+  do {
+    Print.print_rule ppf symbols;
+    Format.pp_print_flush ppf ();
+    raise (Rule_not_found (Buffer.contents b))
+  }
+;
+
 value rec delete_rule_in_suffix entry symbols =
   fun
   [ [lev :: levs] ->
@@ -104,7 +118,7 @@ value rec delete_rule_in_suffix entry symbols =
       | None ->
           let levs = delete_rule_in_suffix entry symbols levs in
           [lev :: levs] ]
-  | [] -> raise Not_found ]
+  | [] -> rule_not_found entry symbols ]
 ;
 
 value rec delete_rule_in_prefix entry symbols =
@@ -128,7 +142,7 @@ value rec delete_rule_in_prefix entry symbols =
       | None ->
           let levs = delete_rule_in_prefix entry symbols levs in
           [lev :: levs] ]
-  | [] -> raise Not_found ]
+  | [] -> rule_not_found entry symbols ]
 ;
 
 value rec delete_rule_in_level_list entry symbols levs =
diff --git camlp4/Camlp4Parsers/Camlp4ListComprehension.ml camlp4/Camlp4Parsers/Camlp4ListComprehension.ml
index 874426b..fa5ee19 100644
--- camlp4/Camlp4Parsers/Camlp4ListComprehension.ml
+++ camlp4/Camlp4Parsers/Camlp4ListComprehension.ml
@@ -102,7 +102,7 @@ module Make (Syntax : Sig.Camlp4Syntax) = struct
     try do {
       DELETE_RULE Gram expr: "["; sem_expr_for_list; "::"; expr; "]" END;
       True
-    } with [ Not_found -> False ];
+    } with [ Struct.Grammar.Delete.Rule_not_found _ -> False ];
 
   value comprehension_or_sem_expr_for_list =
     Gram.Entry.mk "comprehension_or_sem_expr_for_list";
diff --git camlp4/Camlp4Parsers/Camlp4MacroParser.ml camlp4/Camlp4Parsers/Camlp4MacroParser.ml
index 57f660d..20fa7a3 100644
--- camlp4/Camlp4Parsers/Camlp4MacroParser.ml
+++ camlp4/Camlp4Parsers/Camlp4MacroParser.ml
@@ -234,7 +234,7 @@ module Make (Syntax : Sig.Camlp4Syntax) = struct
         defined.val := list_remove x defined.val;
       }
     with
-    [ Not_found -> () ];
+    [ Struct.Grammar.Delete.Rule_not_found _ -> () ];
 
   value parse_def s =
     match Gram.parse_string expr (Loc.mk "<command line>") s with
diff --git camlp4/Camlp4Parsers/Camlp4OCamlReloadedParser.ml camlp4/Camlp4Parsers/Camlp4OCamlReloadedParser.ml
index e56ab36..75016d8 100644
--- camlp4/Camlp4Parsers/Camlp4OCamlReloadedParser.ml
+++ camlp4/Camlp4Parsers/Camlp4OCamlReloadedParser.ml
@@ -40,7 +40,7 @@ module Make (Syntax : Sig.Camlp4Syntax) = struct
   value revised =
     try
       (DELETE_RULE Gram expr: "if"; SELF; "then"; SELF; "else"; SELF END; True)
-    with [ Not_found -> begin
+    with [ Struct.Grammar.Delete.Rule_not_found _ -> begin
       DELETE_RULE Gram expr: "if"; SELF; "then"; expr LEVEL "top"; "else"; expr LEVEL "top" END;
       DELETE_RULE Gram expr: "if"; SELF; "then"; expr LEVEL "top" END; False
     end ];