diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/resteasy/ApiClient.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/resteasy/ApiClient.mustache
index f447d645807..ad1fcc649dd 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/resteasy/ApiClient.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/resteasy/ApiClient.mustache
@@ -638,7 +638,7 @@ public class ApiClient {
 
     for (Entry<String, String> defaultHeaderEnrty: defaultHeaderMap.entrySet()) {
       if (!headerParams.containsKey(defaultHeaderEnrty.getKey())) {
-        String value = defaultHeaderEnrty.getKey();
+        String value = defaultHeaderEnrty.getValue();
         if (value != null) {
           invocationBuilder = invocationBuilder.header(defaultHeaderEnrty.getKey(), value);
         }
diff --git a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/ApiClient.java
index 5e80ded364f..b8cbc485421 100644
--- a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/ApiClient.java
@@ -633,7 +633,7 @@ public class ApiClient {
 
     for (Entry<String, String> defaultHeaderEnrty: defaultHeaderMap.entrySet()) {
       if (!headerParams.containsKey(defaultHeaderEnrty.getKey())) {
-        String value = defaultHeaderEnrty.getKey();
+        String value = defaultHeaderEnrty.getValue();
         if (value != null) {
           invocationBuilder = invocationBuilder.header(defaultHeaderEnrty.getKey(), value);
         }