diff --git a/app/serializers/dossier_serializer.rb b/app/serializers/dossier_serializer.rb
index 869aa727c..dbc3f90e9 100644
--- a/app/serializers/dossier_serializer.rb
+++ b/app/serializers/dossier_serializer.rb
@@ -47,6 +47,11 @@ class DossierSerializer < ActiveModel::Serializer
     []
   end
 
+  def pieces_justificatives
+    ActiveModelSerializers::SerializableResource.new(object.pieces_justificatives).serializable_hash +
+      PiecesJustificativesService.serialize_champs_as_pjs(object)
+  end
+
   def email
     object.user&.email
   end
diff --git a/app/services/pieces_justificatives_service.rb b/app/services/pieces_justificatives_service.rb
index d0bc69815..dd617b28b 100644
--- a/app/services/pieces_justificatives_service.rb
+++ b/app/services/pieces_justificatives_service.rb
@@ -84,4 +84,15 @@ class PiecesJustificativesService
       }
     end
   end
+
+  def self.serialize_champs_as_pjs(dossier)
+    dossier.champs.select { |champ| champ.type_de_champ.old_pj }.map do |champ|
+      {
+        created_at: champ.created_at&.in_time_zone('UTC'),
+        type_de_piece_justificative_id: champ.type_de_champ.old_pj[:stable_id],
+        content_url: champ.for_api,
+        user: champ.dossier.user
+      }
+    end
+  end
 end
diff --git a/spec/serializers/dossier_serializer_spec.rb b/spec/serializers/dossier_serializer_spec.rb
index aa9e51a28..730ea1e56 100644
--- a/spec/serializers/dossier_serializer_spec.rb
+++ b/spec/serializers/dossier_serializer_spec.rb
@@ -45,4 +45,46 @@ describe DossierSerializer do
       }
     end
   end
+
+  context 'when a type PJ was cloned to a type champ PJ' do
+    let(:original_procedure) do
+      p = create(:procedure, :published)
+      p.types_de_piece_justificative.create(
+        libelle: "Vidéo de votre demande de subvention",
+        description: "Pour optimiser vos chances, soignez la chorégraphie et privilégiez le chant polyphonique",
+        lien_demarche: "https://www.dance-academy.gouv.fr",
+        order_place: 0
+      )
+      p
+    end
+
+    let(:procedure) do
+      p = original_procedure.clone(original_procedure.administrateur, false)
+      p.save
+      p
+    end
+
+    let(:type_pj) { original_procedure.types_de_piece_justificative.first }
+    let(:dossier) { create(:dossier, procedure: procedure) }
+    let(:champ_pj) { dossier.champs.last }
+
+    before do
+      champ_pj.piece_justificative_file.attach(io: StringIO.new("toto"), filename: "toto.txt", content_type: "text/plain")
+    end
+
+    subject { DossierSerializer.new(dossier).serializable_hash }
+
+    it "exposes the PJ in the legacy format" do
+      is_expected.to include(
+        pieces_justificatives: [
+          {
+            "content_url" => champ_pj.for_api,
+            "created_at" => champ_pj.created_at.in_time_zone('UTC').iso8601(3),
+            "type_de_piece_justificative_id" => type_pj.id,
+            "user" => a_hash_including("id" => dossier.user.id)
+          }
+        ]
+      )
+    end
+  end
 end