diff --git a/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/ApiClient.java
index 81b1cc166d17..0f00ca520506 100644
--- a/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/ApiClient.java
@@ -67,6 +67,7 @@
 import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.nio.charset.UnsupportedCharsetException;
 import java.nio.file.Files;
 import java.nio.file.StandardCopyOption;
@@ -703,7 +704,7 @@ public HttpEntity serialize(Object obj, Map<String, Object> formParams, ContentT
     String mimeType = contentType.getMimeType();
     if (isJsonMime(mimeType)) {
       try {
-        return new StringEntity(objectMapper.writeValueAsString(obj), contentType);
+        return new StringEntity(objectMapper.writeValueAsString(obj), contentType.withCharset(StandardCharsets.UTF_8));
       } catch (JsonProcessingException e) {
         throw new ApiException(e);
       }
diff --git a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/ApiClient.java
index d92b2555617f..3bce7e0f2caa 100644
--- a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/ApiClient.java
@@ -67,6 +67,7 @@
 import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.nio.charset.UnsupportedCharsetException;
 import java.nio.file.Files;
 import java.nio.file.StandardCopyOption;
@@ -796,7 +797,7 @@ public HttpEntity serialize(Object obj, Map<String, Object> formParams, ContentT
     String mimeType = contentType.getMimeType();
     if (isJsonMime(mimeType)) {
       try {
-        return new StringEntity(objectMapper.writeValueAsString(obj), contentType);
+        return new StringEntity(objectMapper.writeValueAsString(obj), contentType.withCharset(StandardCharsets.UTF_8));
       } catch (JsonProcessingException e) {
         throw new ApiException(e);
       }