diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/restclient/ApiClient.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/restclient/ApiClient.mustache
index e63ea452fadc..3a6906b6eaf0 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/restclient/ApiClient.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/restclient/ApiClient.mustache
@@ -239,9 +239,9 @@ public class ApiClient{{#jsr310}} extends JavaTimeFormatter{{/jsr310}} {
 
         {{#useJackson3}}
         Consumer<HttpMessageConverters.ClientBuilder> messageConverters = builder -> {
-            builder.withJsonConverter(new JacksonJsonHttpMessageConverter(mapper));
+            builder.addCustomConverter(new JacksonJsonHttpMessageConverter(mapper));
             {{#withXml}}
-            builder.withXmlConverter(new JacksonXmlHttpMessageConverter(xmlMapper));
+            builder.addCustomConverter(new JacksonXmlHttpMessageConverter(xmlMapper));
             {{/withXml}}
         };
 
diff --git a/samples/client/petstore/java/restclient-springBoot4-jackson3-jspecify/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/restclient-springBoot4-jackson3-jspecify/src/main/java/org/openapitools/client/ApiClient.java
index ff4f62c709ad..86dd7827abaf 100644
--- a/samples/client/petstore/java/restclient-springBoot4-jackson3-jspecify/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/restclient-springBoot4-jackson3-jspecify/src/main/java/org/openapitools/client/ApiClient.java
@@ -148,7 +148,7 @@ protected void init() {
     public static RestClient.Builder buildRestClientBuilder(JsonMapper mapper) {
 
         Consumer<HttpMessageConverters.ClientBuilder> messageConverters = builder -> {
-            builder.withJsonConverter(new JacksonJsonHttpMessageConverter(mapper));
+            builder.addCustomConverter(new JacksonJsonHttpMessageConverter(mapper));
         };
 
         return RestClient.builder().configureMessageConverters(messageConverters);
diff --git a/samples/client/petstore/java/restclient-springBoot4-jackson3/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/restclient-springBoot4-jackson3/src/main/java/org/openapitools/client/ApiClient.java
index 36fa8815391f..f6fce8ae3f53 100644
--- a/samples/client/petstore/java/restclient-springBoot4-jackson3/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/restclient-springBoot4-jackson3/src/main/java/org/openapitools/client/ApiClient.java
@@ -150,7 +150,7 @@ protected void init() {
     public static RestClient.Builder buildRestClientBuilder(JsonMapper mapper) {
 
         Consumer<HttpMessageConverters.ClientBuilder> messageConverters = builder -> {
-            builder.withJsonConverter(new JacksonJsonHttpMessageConverter(mapper));
+            builder.addCustomConverter(new JacksonJsonHttpMessageConverter(mapper));
         };
 
         return RestClient.builder().configureMessageConverters(messageConverters);