diff --git a/testsuite/tests/typing-local/regression_class_dep.ml b/testsuite/tests/typing-local/regression_class_dep.ml
new file mode 100644
index 00000000000..dcd2a6aeebb
--- /dev/null
+++ b/testsuite/tests/typing-local/regression_class_dep.ml
@@ -0,0 +1,9 @@
+class c =
+  object
+    method private m () () = 0
+  end
+
+class virtual cv =
+  object
+    method virtual private m : unit -> unit -> int
+  end
diff --git a/testsuite/tests/typing-local/regression_class_type.ml b/testsuite/tests/typing-local/regression_class_type.ml
new file mode 100644
index 00000000000..d0c6803e294
--- /dev/null
+++ b/testsuite/tests/typing-local/regression_class_type.ml
@@ -0,0 +1,18 @@
+(* TEST
+readonly_files = "regression_class_dep.ml"
+* setup-ocamlc.opt-build-env
+** ocamlc.opt
+module = "regression_class_dep.ml"
+*** ocamlc.opt
+module = ""
+flags = "-c"
+*)
+
+(* https://github.com/ocaml-flambda/ocaml-jst/issues/65 *)
+
+module Dep = Regression_class_dep
+class c fname =
+  object
+    inherit Dep.c
+    inherit Dep.cv
+  end
diff --git a/typing/ctype.ml b/typing/ctype.ml
index 75ab9412424..0278829507b 100644
--- a/typing/ctype.ml
+++ b/typing/ctype.ml
@@ -5214,6 +5214,7 @@ let rec nongen_schema_rec env ty =
 
 (* Return whether all variables of type [ty] are generic. *)
 let nongen_schema env ty =
+  remove_mode_variables ty;
   visited := TypeSet.empty;
   try
     nongen_schema_rec env ty;
diff --git a/typing/ctype.mli b/typing/ctype.mli
index f900d8a72ce..1c79256e2fd 100644
--- a/typing/ctype.mli
+++ b/typing/ctype.mli
@@ -398,11 +398,12 @@ val remove_mode_variables: type_expr -> unit
 
 val nongen_schema: Env.t -> type_expr -> bool
         (* Check whether the given type scheme contains no non-generic
-           type variables *)
+           type variables, and ensure mode variables are fully determined *)
 
 val nongen_class_declaration: class_declaration -> bool
         (* Check whether the given class type contains no non-generic
-           type variables. Uses the empty environment.  *)
+           type variables, and ensures mode variables are fully determined.
+           Uses the empty environment.  *)
 
 val free_variables: ?env:Env.t -> type_expr -> type_expr list
         (* If env present, then check for incomplete definitions too *)
diff --git a/typing/typemod.ml b/typing/typemod.ml
index 2684f80d33d..abef4d95550 100644
--- a/typing/typemod.ml
+++ b/typing/typemod.ml
@@ -1938,17 +1938,13 @@ and nongen_signature_item env f = function
   | Sig_module(_id, _, md, _, _) -> nongen_modtype env f md.md_type
   | _ -> false
 
-let nongen_ty env ty =
-  Ctype.remove_mode_variables ty;
-  Ctype.nongen_schema env ty
-
 let check_nongen_signature_item env sig_item =
   match sig_item with
     Sig_value(_id, vd, _) ->
-      if nongen_ty env vd.val_type then
+      if Ctype.nongen_schema env vd.val_type then
         raise (Error (vd.val_loc, env, Non_generalizable vd.val_type))
   | Sig_module (_id, _, md, _, _) ->
-      if nongen_modtype env nongen_ty md.md_type then
+      if nongen_modtype env Ctype.nongen_schema md.md_type then
         raise(Error(md.md_loc, env, Non_generalizable_module md.md_type))
   | _ -> ()
 
@@ -2983,7 +2979,7 @@ let type_module_type_of env smod =
   in
   let mty = Mtype.scrape_for_type_of ~remove_aliases env tmty.mod_type in
   (* PR#5036: must not contain non-generalized type variables *)
-  if nongen_modtype env nongen_ty mty then
+  if nongen_modtype env Ctype.nongen_schema mty then
     raise(Error(smod.pmod_loc, env, Non_generalizable_module mty));
   tmty, mty