diff --git a/app/graphql/schema.graphql b/app/graphql/schema.graphql
index da40645a5..a4820a002 100644
--- a/app/graphql/schema.graphql
+++ b/app/graphql/schema.graphql
@@ -1131,7 +1131,8 @@ type Entreprise {
 }
 
 type File {
-  byteSize: Int!
+  byteSize: Int! @deprecated(reason: "Utilisez le champ `byteSizeBigInt` à la place.")
+  byteSizeBigInt: BigInt!
   checksum: String!
   contentType: String!
   filename: String!
diff --git a/app/graphql/types/file.rb b/app/graphql/types/file.rb
index 0fc4cf1bd..22a8e1afd 100644
--- a/app/graphql/types/file.rb
+++ b/app/graphql/types/file.rb
@@ -2,7 +2,8 @@ module Types
   class File < Types::BaseObject
     field :url, Types::URL, null: false
     field :filename, String, null: false
-    field :byte_size, Int, null: false
+    field :byte_size, Int, null: false, deprecation_reason: "Utilisez le champ `byteSizeBigInt` à la place."
+    field :byte_size_big_int, GraphQL::Types::BigInt, null: false, method: :byte_size
     field :checksum, String, null: false
     field :content_type, String, null: false
 
diff --git a/app/services/serializer_service.rb b/app/services/serializer_service.rb
index 04d816f3c..3ded29254 100644
--- a/app/services/serializer_service.rb
+++ b/app/services/serializer_service.rb
@@ -232,7 +232,7 @@ class SerializerService
     fragment FileFragment on File {
       filename
       checksum
-      byteSize
+      byteSize: byteSizeBigInt
       contentType
     }
   GRAPHQL
diff --git a/spec/controllers/api/v2/graphql_controller_spec.rb b/spec/controllers/api/v2/graphql_controller_spec.rb
index e732ec43a..8e2a3ae0b 100644
--- a/spec/controllers/api/v2/graphql_controller_spec.rb
+++ b/spec/controllers/api/v2/graphql_controller_spec.rb
@@ -649,6 +649,73 @@ describe API::V2::GraphqlController do
       end
     end
 
+    context "champ" do
+      let(:champ) { create(:champ_piece_justificative, dossier: dossier) }
+      let(:byte_size) { 2712286911 }
+
+      context "byteSize" do
+        let(:query) do
+          "{
+            dossier(number: #{dossier.id}) {
+              champs(id: \"#{champ.to_typed_id}\") {
+                ... on PieceJustificativeChamp {
+                  file { byteSize }
+                }
+              }
+            }
+          }"
+        end
+
+        it {
+          expect(gql_errors).to be_nil
+          expect(gql_data).to eq(dossier: { champs: [{ file: { byteSize: 4 } }] })
+        }
+      end
+
+      context "when file is really big" do
+        before do
+          champ.piece_justificative_file.blob.update(byte_size: byte_size)
+        end
+
+        context "byteSize" do
+          let(:query) do
+            "{
+              dossier(number: #{dossier.id}) {
+                champs(id: \"#{champ.to_typed_id}\") {
+                  ... on PieceJustificativeChamp {
+                    file { byteSize }
+                  }
+                }
+              }
+            }"
+          end
+
+          it {
+            expect(gql_errors).not_to be_nil
+          }
+        end
+
+        context "byteSizeBigInt" do
+          let(:query) do
+            "{
+              dossier(number: #{dossier.id}) {
+                champs(id: \"#{champ.to_typed_id}\") {
+                  ... on PieceJustificativeChamp {
+                    file { byteSizeBigInt }
+                  }
+                }
+              }
+            }"
+          end
+
+          it {
+            expect(gql_errors).to be_nil
+            expect(gql_data).to eq(dossier: { champs: [{ file: { byteSizeBigInt: '2712286911' } }] })
+          }
+        end
+      end
+    end
+
     context "groupeInstructeur" do
       let(:groupe_instructeur) { procedure.groupe_instructeurs.first }
       let(:query) do