diff --git a/src/main/resources/handlebars/Java/libraries/resttemplate/ApiClient.mustache b/src/main/resources/handlebars/Java/libraries/resttemplate/ApiClient.mustache
index c74ff62c8f..23dba3dc7e 100644
--- a/src/main/resources/handlebars/Java/libraries/resttemplate/ApiClient.mustache
+++ b/src/main/resources/handlebars/Java/libraries/resttemplate/ApiClient.mustache
@@ -250,7 +250,7 @@ public class ApiClient {
      * @return ApiClient this client
      */
     public ApiClient addDefaultHeader(String name, String value) {
-        defaultHeaders.add(name, value);
+        defaultHeaders.set(name, value);
         return this;
     }