diff --git a/extensions/resteasy-reactive/rest/deployment/src/test/java/io/quarkus/resteasy/reactive/server/test/multipart/MultipartOutputResource.java b/extensions/resteasy-reactive/rest/deployment/src/test/java/io/quarkus/resteasy/reactive/server/test/multipart/MultipartOutputResource.java
index 2c0971ff4401a..0bbf3f08a6be5 100644
--- a/extensions/resteasy-reactive/rest/deployment/src/test/java/io/quarkus/resteasy/reactive/server/test/multipart/MultipartOutputResource.java
+++ b/extensions/resteasy-reactive/rest/deployment/src/test/java/io/quarkus/resteasy/reactive/server/test/multipart/MultipartOutputResource.java
@@ -60,6 +60,7 @@ public RestResponse<MultipartFormDataOutput> withFormDataOutput() {
         MultipartFormDataOutput form = new MultipartFormDataOutput();
         form.addFormData("name", RESPONSE_NAME, MediaType.TEXT_PLAIN_TYPE);
         form.addFormData("part-with-filename", RESPONSE_FILENAME, MediaType.TEXT_PLAIN_TYPE, "file.txt");
+        form.addFormData("part-with-filename", RESPONSE_FILENAME, MediaType.TEXT_PLAIN_TYPE, "file2.txt");
         form.addFormData("custom-surname", RESPONSE_SURNAME, MediaType.TEXT_PLAIN_TYPE);
         form.addFormData("custom-status", RESPONSE_STATUS, MediaType.TEXT_PLAIN_TYPE)
                 .getHeaders().putSingle("extra-header", "extra-value");
diff --git a/extensions/resteasy-reactive/rest/deployment/src/test/java/io/quarkus/resteasy/reactive/server/test/multipart/MultipartOutputUsingBlockingEndpointsTest.java b/extensions/resteasy-reactive/rest/deployment/src/test/java/io/quarkus/resteasy/reactive/server/test/multipart/MultipartOutputUsingBlockingEndpointsTest.java
index a631ec0f25390..d1a1b3032726f 100644
--- a/extensions/resteasy-reactive/rest/deployment/src/test/java/io/quarkus/resteasy/reactive/server/test/multipart/MultipartOutputUsingBlockingEndpointsTest.java
+++ b/extensions/resteasy-reactive/rest/deployment/src/test/java/io/quarkus/resteasy/reactive/server/test/multipart/MultipartOutputUsingBlockingEndpointsTest.java
@@ -75,6 +75,7 @@ public void testWithFormData() {
         String body = extractable.asString();
         assertContainsValue(body, "name", MediaType.TEXT_PLAIN, MultipartOutputResource.RESPONSE_NAME);
         assertContainsValue(body, "part-with-filename", MediaType.TEXT_PLAIN, "filename=\"file.txt\"");
+        assertContainsValue(body, "part-with-filename", MediaType.TEXT_PLAIN, "filename=\"file2.txt\"");
         assertContainsValue(body, "custom-surname", MediaType.TEXT_PLAIN, MultipartOutputResource.RESPONSE_SURNAME);
         assertContainsValue(body, "custom-status", MediaType.TEXT_PLAIN, MultipartOutputResource.RESPONSE_STATUS);
         assertContainsValue(body, "active", MediaType.TEXT_PLAIN, MultipartOutputResource.RESPONSE_ACTIVE);
diff --git a/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/core/multipart/MultipartMessageBodyWriter.java b/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/core/multipart/MultipartMessageBodyWriter.java
index 6896e96e67225..2c8750777dbba 100644
--- a/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/core/multipart/MultipartMessageBodyWriter.java
+++ b/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/core/multipart/MultipartMessageBodyWriter.java
@@ -85,21 +85,27 @@ private void write(MultipartFormDataOutput formDataOutput, String boundary, Outp
             throws IOException {
         Charset charset = requestContext.getDeployment().getRuntimeConfiguration().body().defaultCharset();
         String boundaryLine = "--" + boundary;
-        Map<String, PartItem> parts = formDataOutput.getFormData();
-        for (Map.Entry<String, PartItem> entry : parts.entrySet()) {
+        Map<String, List<PartItem>> parts = formDataOutput.getAllFormData();
+        for (var entry : parts.entrySet()) {
             String partName = entry.getKey();
-            PartItem part = entry.getValue();
-            Object partValue = part.getEntity();
-            if (partValue != null) {
-                if (isListOf(part, File.class) || isListOf(part, FileDownload.class)) {
-                    List<Object> list = (List<Object>) partValue;
-                    for (int i = 0; i < list.size(); i++) {
-                        writePart(partName, list.get(i), part, boundaryLine, charset, outputStream, requestContext);
+            List<PartItem> partItems = entry.getValue();
+            if (partItems.isEmpty()) {
+                continue;
+            }
+            for (PartItem part : partItems) {
+                Object partValue = part.getEntity();
+                if (partValue != null) {
+                    if (isListOf(part, File.class) || isListOf(part, FileDownload.class)) {
+                        List<Object> list = (List<Object>) partValue;
+                        for (int i = 0; i < list.size(); i++) {
+                            writePart(partName, list.get(i), part, boundaryLine, charset, outputStream, requestContext);
+                        }
+                    } else {
+                        writePart(partName, partValue, part, boundaryLine, charset, outputStream, requestContext);
                     }
-                } else {
-                    writePart(partName, partValue, part, boundaryLine, charset, outputStream, requestContext);
                 }
             }
+
         }
 
         // write boundary: -- ... --
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 3b8212907a3ca..baccd98c55cc5 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 +1,9 @@
 package org.jboss.resteasy.reactive.server.multipart;
 
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.LinkedHashMap;
+import java.util.List;
 import java.util.Map;
 
 import jakarta.ws.rs.core.MediaType;
@@ -10,9 +12,26 @@
  * Used when a Resource method needs to return a multipart output
  */
 public final class MultipartFormDataOutput {
-    private final Map<String, PartItem> parts = new LinkedHashMap<>();
+    private final Map<String, List<PartItem>> parts = new LinkedHashMap<>();
 
+    /**
+     * @deprecated use {@link #getAllFormData()} instead
+     */
+    @Deprecated(forRemoval = true)
     public Map<String, PartItem> getFormData() {
+        Map<String, PartItem> result = new LinkedHashMap<>();
+        for (var entry : parts.entrySet()) {
+            if (entry.getValue().isEmpty()) {
+                continue;
+            }
+            // use the last item inserted as this is the old behavior
+            int lastIndex = entry.getValue().size() - 1;
+            result.put(entry.getKey(), entry.getValue().get(lastIndex));
+        }
+        return Collections.unmodifiableMap(result);
+    }
+
+    public Map<String, List<PartItem>> getAllFormData() {
         return Collections.unmodifiableMap(parts);
     }
 
@@ -31,7 +50,8 @@ public PartItem addFormData(String key, Object entity, MediaType mediaType, Stri
     }
 
     private PartItem addFormData(String key, PartItem part) {
-        parts.put(key, part);
+        List<PartItem> items = parts.computeIfAbsent(key, k -> new ArrayList<>());
+        items.add(part);
         return part;
     }
 }