diff --git a/src/server/actix_listener.rs b/src/server/actix_listener.rs
index b1fe468..8054968 100644
--- a/src/server/actix_listener.rs
+++ b/src/server/actix_listener.rs
@@ -195,7 +195,7 @@ impl Into<actix_web::HttpResponse> for HttpResponse {
         );
 
         for (key, value) in self.headers {
-            builder.insert_header((key, value));
+            builder.append_header((key, value));
         }
 
         builder.body(self.body)