diff --git a/modules/openapi-generator/src/main/resources/scala-akka-client/apiInvoker.mustache b/modules/openapi-generator/src/main/resources/scala-akka-client/apiInvoker.mustache
index 5999fe09821..8c81b0b2d8b 100644
--- a/modules/openapi-generator/src/main/resources/scala-akka-client/apiInvoker.mustache
+++ b/modules/openapi-generator/src/main/resources/scala-akka-client/apiInvoker.mustache
@@ -103,11 +103,11 @@ class ApiInvoker(formats: Formats)(implicit system: ActorSystem) extends CustomC
     request: HttpRequest =>
       credentialsSeq.foldLeft(request) {
         case (req, BasicCredentials(login, password)) =>
-          req.withHeaders(Authorization(BasicHttpCredentials(login, password)))
+          req.addHeader(Authorization(BasicHttpCredentials(login, password)))
         case (req, ApiKeyCredentials(keyValue, keyName, ApiKeyLocations.HEADER)) =>
-          req.withHeaders(RawHeader(keyName, keyValue.value))
+          req.addHeader(RawHeader(keyName, keyValue.value))
         case (req, BearerToken(token)) =>
-            req.withHeaders(RawHeader("Authorization", s"Bearer $token"))
+            req.addHeader(RawHeader("Authorization", s"Bearer $token"))
         case (req, _) => req
       }
   }
diff --git a/samples/client/petstore/scala-akka/src/main/scala/org/openapitools/client/core/ApiInvoker.scala b/samples/client/petstore/scala-akka/src/main/scala/org/openapitools/client/core/ApiInvoker.scala
index 3e6c1dbeb44..d3ff4cadb8e 100644
--- a/samples/client/petstore/scala-akka/src/main/scala/org/openapitools/client/core/ApiInvoker.scala
+++ b/samples/client/petstore/scala-akka/src/main/scala/org/openapitools/client/core/ApiInvoker.scala
@@ -113,11 +113,11 @@ class ApiInvoker(formats: Formats)(implicit system: ActorSystem) extends CustomC
     request: HttpRequest =>
       credentialsSeq.foldLeft(request) {
         case (req, BasicCredentials(login, password)) =>
-          req.withHeaders(Authorization(BasicHttpCredentials(login, password)))
+          req.addHeader(Authorization(BasicHttpCredentials(login, password)))
         case (req, ApiKeyCredentials(keyValue, keyName, ApiKeyLocations.HEADER)) =>
-          req.withHeaders(RawHeader(keyName, keyValue.value))
+          req.addHeader(RawHeader(keyName, keyValue.value))
         case (req, BearerToken(token)) =>
-            req.withHeaders(RawHeader("Authorization", s"Bearer $token"))
+            req.addHeader(RawHeader("Authorization", s"Bearer $token"))
         case (req, _) => req
       }
   }