diff --git a/src/Kontur.Extern.Api.Client/ApiLevel/Json/JsonSerializerFactory.cs b/src/Kontur.Extern.Api.Client/ApiLevel/Json/JsonSerializerFactory.cs
index dc19ad66..90363413 100644
--- a/src/Kontur.Extern.Api.Client/ApiLevel/Json/JsonSerializerFactory.cs
+++ b/src/Kontur.Extern.Api.Client/ApiLevel/Json/JsonSerializerFactory.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Text.Json;
 using Kontur.Extern.Api.Client.ApiLevel.Json.Converters;
 using Kontur.Extern.Api.Client.ApiLevel.Json.Converters.Docflows;
@@ -16,11 +17,14 @@ namespace Kontur.Extern.Api.Client.ApiLevel.Json
 {
     public static class JsonSerializerFactory
     {
-        public static IJsonSerializer CreateJsonSerializer(ILog log, bool ignoreIndentation = false, bool ignoreNullValues = true)
+        public static IJsonSerializer CreateJsonSerializer(ILog log, bool ignoreIndentation = false, bool ignoreNullValues = true, Func<SystemTextJsonSerializerFactory>? setupSerializer = null)
         {
             var namingPolicy = new KebabCaseNamingPolicy();
-            return new SystemTextJsonSerializerFactory()
-                .WithNamingPolicy(namingPolicy)
+            var factory = new SystemTextJsonSerializerFactory();
+            if (setupSerializer is not null)
+                factory = setupSerializer();
+
+            return factory.WithNamingPolicy(namingPolicy)
                 .AddConverter(new UrnJsonConverter())
                 .AddConverter(new StringBasedValueTypesConverter())
                 .AddConverter(new DocflowConverter())
diff --git a/src/Kontur.Extern.Api.Client/ExternFactory.cs b/src/Kontur.Extern.Api.Client/ExternFactory.cs
index 456a6338..80da025f 100644
--- a/src/Kontur.Extern.Api.Client/ExternFactory.cs
+++ b/src/Kontur.Extern.Api.Client/ExternFactory.cs
@@ -16,6 +16,7 @@
 using Kontur.Extern.Api.Client.Http.Configurations;
 using Kontur.Extern.Api.Client.Http.Options;
 using Kontur.Extern.Api.Client.Http.Serialization;
+using Kontur.Extern.Api.Client.Http.Serialization.SysTextJson;
 using Vostok.Clusterclient.Core.Model;
 using Vostok.Commons.Time;
 using Vostok.Logging.Abstractions;
@@ -38,14 +39,15 @@ public IExtern Create(
             IAuthenticator authenticator,
             IExternHttpClient? api,
             IHttpRequestFactory? httpRequestFactory,
-            ILog log)
+            ILog log,
+            Func<SystemTextJsonSerializerFactory>? setupSerializer = null)
         {
             contentManagementOptions ??= ContentManagementOptions.Default;
             pollingStrategy ??= DefaultDelayPollingStrategy;
             cryptoProvider ??= DefaultCryptoProvider;
             requestTimeouts ??= new RequestTimeouts();
 
-            var jsonSerializer = JsonSerializerFactory.CreateJsonSerializer(log);
+            var jsonSerializer = JsonSerializerFactory.CreateJsonSerializer(log, setupSerializer: setupSerializer);
             httpRequestFactory ??= CreateHttp(clientConfiguration, requestTimeouts, authenticator, jsonSerializer, log);
             api ??= new ExternHttpClient(httpRequestFactory);
             var services = new ExternClientServices(contentManagementOptions, httpRequestFactory, jsonSerializer, api, pollingStrategy, authenticator, cryptoProvider);