diff --git a/infer/src/clang/cGeneral_utils.ml b/infer/src/clang/cGeneral_utils.ml
index 3577f6235..90cedfa60 100644
--- a/infer/src/clang/cGeneral_utils.ml
+++ b/infer/src/clang/cGeneral_utils.ml
@@ -30,20 +30,11 @@ let rec string_from_list l =
   match l with [] -> "" | [item] -> item | item :: l' -> item ^ " " ^ string_from_list l'
 
 
-let rec append_no_duplicates eq list1 list2 =
-  match list2 with
-  | el :: rest2 ->
-      if List.mem ~equal:eq list1 el then append_no_duplicates eq list1 rest2
-      else append_no_duplicates eq list1 rest2 @ [el]
-  | [] ->
-      list1
-
-
-let append_no_duplicates_csu list1 list2 = append_no_duplicates Typ.Name.equal list1 list2
-
 let append_no_duplicates_annotations list1 list2 =
-  let eq (annot1, _) (annot2, _) = String.equal annot1.Annot.class_name annot2.Annot.class_name in
-  append_no_duplicates eq list1 list2
+  let equal (annot1, _) (annot2, _) =
+    String.equal annot1.Annot.class_name annot2.Annot.class_name
+  in
+  IList.append_no_duplicates equal list1 list2
 
 
 let add_no_duplicates_fields field_tuple l =
@@ -201,4 +192,3 @@ let mk_sil_var trans_unit_ctx named_decl_info decl_info_qual_type_opt procname o
         CAst_utils.get_qualified_name named_decl_info |> QualifiedCppName.to_qual_string
       in
       Pvar.mk (Mangled.from_string name_string) procname
-
diff --git a/infer/src/clang/cGeneral_utils.mli b/infer/src/clang/cGeneral_utils.mli
index 44fb8ab48..dce413599 100644
--- a/infer/src/clang/cGeneral_utils.mli
+++ b/infer/src/clang/cGeneral_utils.mli
@@ -19,8 +19,6 @@ val append_no_duplicates_fields :
   (Typ.Fieldname.t * Typ.t * Annot.Item.t) list -> (Typ.Fieldname.t * Typ.t * Annot.Item.t) list
   -> (Typ.Fieldname.t * Typ.t * Annot.Item.t) list
 
-val append_no_duplicates_csu : Typ.Name.t list -> Typ.Name.t list -> Typ.Name.t list
-
 val collect_list_tuples :
   ('a list * 'b list * 'c list * 'd list * 'e list) list
   -> 'a list * 'b list * 'c list * 'd list * 'e list
diff --git a/infer/src/clang/objcInterface_decl.ml b/infer/src/clang/objcInterface_decl.ml
index 85e1426a9..c2a4cbfa8 100644
--- a/infer/src/clang/objcInterface_decl.ml
+++ b/infer/src/clang/objcInterface_decl.ml
@@ -111,7 +111,7 @@ let add_class_to_tenv qual_type_to_sil_type tenv decl_info name_info decl_list o
     match Tenv.lookup tenv interface_name with
     | Some {fields; supers} ->
         ( CGeneral_utils.append_no_duplicates_fields decl_fields fields
-        , CGeneral_utils.append_no_duplicates_csu decl_supers supers )
+        , IList.append_no_duplicates Typ.Name.equal decl_supers supers )
     | _ ->
         (decl_fields, decl_supers)
   in
@@ -177,4 +177,3 @@ let interface_impl_declaration qual_type_to_sil_type tenv decl =
       class_desc
   | _ ->
       assert false
-
diff --git a/infer/src/istd/IList.ml b/infer/src/istd/IList.ml
index f66b793a6..20a2f8fad 100644
--- a/infer/src/istd/IList.ml
+++ b/infer/src/istd/IList.ml
@@ -102,3 +102,7 @@ let to_string f l =
 
 
 let uncons_exn = function [] -> failwith "uncons_exn" | hd :: tl -> (hd, tl)
+
+let append_no_duplicates eq list1 list2 =
+  let list2_no_dup = List.filter (fun x2 -> List.for_all (fun x1 -> not (eq x2 x1)) list1) list2 in
+  list1 @ list2_no_dup
diff --git a/infer/src/istd/IList.mli b/infer/src/istd/IList.mli
index c4e004dcb..540cbc95a 100644
--- a/infer/src/istd/IList.mli
+++ b/infer/src/istd/IList.mli
@@ -30,3 +30,8 @@ val to_string : ('a -> string) -> 'a list -> string
 
 val uncons_exn : 'a list -> 'a * 'a list
 (** deconstruct a list, like hd_exn and tl_exn *)
+
+val append_no_duplicates : ('a -> 'a -> bool) -> 'a list -> 'a list -> 'a list
+(** [append_no_duplicates list1 list2], assuming that list1 and list2 have no duplicates on their own,
+   it computes list1 @ (filtered list2), so it keeps the order of both lists and has no duplicates.
+   However, the complexity is O(n^2), don't use for big lists!  *)