diff --git a/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/multipart/MultipartFormDataOutput.java b/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/multipart/MultipartFormDataOutput.java
index df175a86839c8..3b8212907a3ca 100644
--- a/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/multipart/MultipartFormDataOutput.java
+++ b/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/multipart/MultipartFormDataOutput.java
@@ -1,7 +1,7 @@
 package org.jboss.resteasy.reactive.server.multipart;
 
 import java.util.Collections;
-import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.Map;
 
 import jakarta.ws.rs.core.MediaType;
@@ -10,7 +10,7 @@
  * Used when a Resource method needs to return a multipart output
  */
 public final class MultipartFormDataOutput {
-    private final Map<String, PartItem> parts = new HashMap<>();
+    private final Map<String, PartItem> parts = new LinkedHashMap<>();
 
     public Map<String, PartItem> getFormData() {
         return Collections.unmodifiableMap(parts);