diff --git a/CHANGES.md b/CHANGES.md
index b1ba7426..64788bf1 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,7 @@
 # Unreleased
 
+- Add a comment warning that the file is generated
+  [\#198](https://github.com/ocaml-gospel/ortac/pull/198)
 - Add an include option to qcheck-stm cli
   [\#181](https://github.com/ocaml-gospel/ortac/pull/181)
 - Add a quiet flag
diff --git a/examples/lwt_dllist_tests.ml b/examples/lwt_dllist_tests.ml
index b1f6b4cf..1f4da0fd 100644
--- a/examples/lwt_dllist_tests.ml
+++ b/examples/lwt_dllist_tests.ml
@@ -1,3 +1,5 @@
+(* This file is generated by ortac qcheck-stm,
+   edit how you run the tool instead *)
 open Lwt_dllist_spec
 module Spec =
   struct
diff --git a/examples/varray_circular_tests.ml b/examples/varray_circular_tests.ml
index eaf06d96..47d9b8f0 100644
--- a/examples/varray_circular_tests.ml
+++ b/examples/varray_circular_tests.ml
@@ -1,3 +1,5 @@
+(* This file is generated by ortac qcheck-stm,
+   edit how you run the tool instead *)
 open Varray_circular_spec
 let inside i s =
   try
diff --git a/examples/varray_tests.ml b/examples/varray_tests.ml
index 4afd74a6..5792c04e 100644
--- a/examples/varray_tests.ml
+++ b/examples/varray_tests.ml
@@ -1,3 +1,5 @@
+(* This file is generated by ortac qcheck-stm,
+   edit how you run the tool instead *)
 open Varray_spec
 let inside i s =
   try
diff --git a/plugins/qcheck-stm/src/reserr.ml b/plugins/qcheck-stm/src/reserr.ml
index 50c004c6..f03141a2 100644
--- a/plugins/qcheck-stm/src/reserr.ml
+++ b/plugins/qcheck-stm/src/reserr.ml
@@ -224,7 +224,11 @@ let pp quiet pp_ok ppf r =
   let open Fmt in
   match r with
   | Ok a, warns -> (
-      pf ppf "%a@." pp_ok a;
+      pf ppf
+        "(* This file is generated by ortac qcheck-stm,@\n\
+        \   edit how you run the tool instead *)@\n\
+         %a@."
+        pp_ok a;
       if not quiet then
         match warns with [] -> () | warns -> pf stderr "%a@." pp_errors warns)
   | Error errs, warns -> pf stderr "%a@." pp_errors (errs @ warns)
diff --git a/plugins/qcheck-stm/test/array_stm_tests.expected.ml b/plugins/qcheck-stm/test/array_stm_tests.expected.ml
index b451e3cf..3ac43b83 100644
--- a/plugins/qcheck-stm/test/array_stm_tests.expected.ml
+++ b/plugins/qcheck-stm/test/array_stm_tests.expected.ml
@@ -1,3 +1,5 @@
+(* This file is generated by ortac qcheck-stm,
+   edit how you run the tool instead *)
 open Array
 module Spec =
   struct
diff --git a/plugins/qcheck-stm/test/conjunctive_clauses_stm_tests.expected.ml b/plugins/qcheck-stm/test/conjunctive_clauses_stm_tests.expected.ml
index 8a7e9cab..73d2e5d0 100644
--- a/plugins/qcheck-stm/test/conjunctive_clauses_stm_tests.expected.ml
+++ b/plugins/qcheck-stm/test/conjunctive_clauses_stm_tests.expected.ml
@@ -1,3 +1,5 @@
+(* This file is generated by ortac qcheck-stm,
+   edit how you run the tool instead *)
 open Conjunctive_clauses
 let set_contents c i a_1 =
   try
diff --git a/plugins/qcheck-stm/test/hashtbl_stm_tests.expected.ml b/plugins/qcheck-stm/test/hashtbl_stm_tests.expected.ml
index ce7456ad..772f5c2b 100644
--- a/plugins/qcheck-stm/test/hashtbl_stm_tests.expected.ml
+++ b/plugins/qcheck-stm/test/hashtbl_stm_tests.expected.ml
@@ -1,3 +1,5 @@
+(* This file is generated by ortac qcheck-stm,
+   edit how you run the tool instead *)
 open Hashtbl
 let rec remove_first x xs_1 =
   try
diff --git a/plugins/qcheck-stm/test/record_stm_tests.expected.ml b/plugins/qcheck-stm/test/record_stm_tests.expected.ml
index f0507bdc..c667fa32 100644
--- a/plugins/qcheck-stm/test/record_stm_tests.expected.ml
+++ b/plugins/qcheck-stm/test/record_stm_tests.expected.ml
@@ -1,3 +1,5 @@
+(* This file is generated by ortac qcheck-stm,
+   edit how you run the tool instead *)
 open Record
 let plus1_1 i =
   try
diff --git a/plugins/qcheck-stm/test/ref_stm_tests.expected.ml b/plugins/qcheck-stm/test/ref_stm_tests.expected.ml
index 79dd5d58..5881bc54 100644
--- a/plugins/qcheck-stm/test/ref_stm_tests.expected.ml
+++ b/plugins/qcheck-stm/test/ref_stm_tests.expected.ml
@@ -1,3 +1,5 @@
+(* This file is generated by ortac qcheck-stm,
+   edit how you run the tool instead *)
 open Ref
 module Spec =
   struct
diff --git a/plugins/qcheck-stm/test/sequence_model_stm_tests.expected.ml b/plugins/qcheck-stm/test/sequence_model_stm_tests.expected.ml
index 2ffaf3cf..a5a95fbe 100644
--- a/plugins/qcheck-stm/test/sequence_model_stm_tests.expected.ml
+++ b/plugins/qcheck-stm/test/sequence_model_stm_tests.expected.ml
@@ -1,3 +1,5 @@
+(* This file is generated by ortac qcheck-stm,
+   edit how you run the tool instead *)
 open Sequence_model
 let length_opt s =
   try Some (Ortac_runtime.Gospelstdlib.Sequence.length s)