diff --git a/CHANGES.md b/CHANGES.md
index f33f0967..a8fde2c6 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,4 +1,10 @@
-## unreleased
+## Version 0.19.2
+
+ - [serlib] Fix (@ejgallego, #398, fixes #397 fixes sr-lab/coqpyt#35 ,
+            thanks to @laetitia-teo and @Nfsaavedra for the bug
+            report)
+
+## Version 0.19.1
 
  - [serlib] Support `btauto` Coq plugin (@ejgallego, #362)
  - [serlib] Support `extraction` Coq plugin (@ejgallego, @toku-sa-n,
diff --git a/serlib/ser_cPrimitives.ml b/serlib/ser_cPrimitives.ml
index 1dc87cea..8b21b0bf 100644
--- a/serlib/ser_cPrimitives.ml
+++ b/serlib/ser_cPrimitives.ml
@@ -16,10 +16,12 @@
 (* Written by: Emilio J. Gallego Arias and others                       *)
 (************************************************************************)
 
-open Sexplib
-open Sexplib.Std
-open Ppx_hash_lib.Std.Hash.Builtin
-open Ppx_compare_lib.Builtin
+(* open Sexplib *)
+(* open Sexplib.Std *)
+(* open Ppx_hash_lib.Std.Hash.Builtin *)
+(* open Ppx_compare_lib.Builtin *)
+
+module UVars = Ser_uvars
 
 type t =
   [%import: CPrimitives.t]
@@ -27,42 +29,45 @@ type t =
 
 type const =
   [%import: CPrimitives.const]
-  [@@deriving sexp,yojson,hash]
+  [@@deriving sexp,yojson,hash,compare]
+
+(* GADTs ... *)
+module PTP = struct
 
-(* XXX: GADTs ... *)
-type 'a prim_type = [%import: 'a CPrimitives.prim_type]
-and 'a prim_ind = [%import: 'a CPrimitives.prim_ind]
-and ind_or_type = [%import: CPrimitives.ind_or_type]
-  [@@deriving sexp_of]
+  type 'a t = 'a CPrimitives.prim_type
 
-let prim_type_of_sexp (x : Sexp.t) : 'a prim_type =
-  match x with
-  | Sexp.Atom "PT_int63" ->
-    PT_int63
-  | Sexp.Atom "PT_float64" ->
-    PT_float64
-  | Sexp.Atom "PT_array" ->
-    Obj.magic PT_array
-  | _ ->
-    Sexplib.Conv_error.no_variant_match ()
+  [@@@ocaml.warning "-27"]
 
-type op_or_type = [%import: CPrimitives.op_or_type]
-  [@@deriving sexp_of]
+  (* Non-GADT version *)
+  type 'a _t =
+    | PT_int63
+    | PT_float64
+    | PT_array
+  [@@deriving sexp,yojson,hash,compare]
+end
 
-let hash_fold_op_or_type st x = hash_fold_string st (Sexp.to_string (sexp_of_op_or_type x))
-let compare_op_or_type x y = compare_string (Sexp.to_string (sexp_of_op_or_type x)) (Sexp.to_string (sexp_of_op_or_type y))
+module Prim_type_ = SerType.Pierce1(PTP)
+type 'a prim_type = 'a Prim_type_.t
+  [@@deriving sexp,yojson,hash,compare]
 
-let op_or_type_of_sexp (x : Sexp.t) : op_or_type =
-  match x with
-  | Sexp.List [Sexp.Atom "OT_op"; p] ->
-    OT_op (t_of_sexp p)
-  | Sexp.List [Sexp.Atom "OT_type"; p] ->
-    OT_type (prim_type_of_sexp p)
-  | Sexp.List [Sexp.Atom "OT_const"; p] ->
-    OT_const (const_of_sexp p)
-  | _ ->
-    Sexplib.Conv_error.no_variant_match ()
+module OOTP = struct
 
-(* XXX *)
-let op_or_type_to_yojson = Obj.magic
-let op_or_type_of_yojson = Obj.magic
+  type ptype =
+    | PT_int63
+    | PT_float64
+    | PT_array
+  [@@deriving sexp,yojson,hash,compare]
+
+  (* op_or_type *)
+  type _t =
+    | OT_op of t
+    | OT_type of ptype
+    | OT_const of const
+  [@@deriving sexp,yojson,hash,compare]
+
+  type t = CPrimitives.op_or_type
+end
+
+module Op_or_type_ = SerType.Pierce(OOTP)
+type op_or_type = Op_or_type_.t
+  [@@deriving sexp,yojson,hash,compare]
diff --git a/tests/genarg/dune b/tests/genarg/dune
index 11ec5940..f1253f9e 100644
--- a/tests/genarg/dune
+++ b/tests/genarg/dune
@@ -161,3 +161,8 @@
  (alias runtest)
  (deps (:input tactic_notation.v))
  (action (run ./test_roundtrip %{input})))
+
+(rule
+ (alias runtest)
+ (deps (:input primitives.v))
+ (action (run ./test_roundtrip %{input})))
diff --git a/tests/genarg/primitives.v b/tests/genarg/primitives.v
new file mode 100644
index 00000000..80608368
--- /dev/null
+++ b/tests/genarg/primitives.v
@@ -0,0 +1,11 @@
+Require Export CarryType.
+
+Primitive int := #int63_type.
+Primitive lsl := #int63_lsl.
+
+Set Universe Polymorphism.
+
+Primitive array := #array_type.
+
+Primitive make : forall A, int -> A -> array A := #array_make.
+Arguments make {_} _ _.