diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/AbstractHttpData.java b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/AbstractHttpData.java
index 39cbde8ffd5..406fc0871ae 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/AbstractHttpData.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/AbstractHttpData.java
@@ -83,7 +83,11 @@ public boolean isCompleted() {
     }
 
     protected void setCompleted() {
-        completed = true;
+        setCompleted(true);
+    }
+
+    protected void setCompleted(boolean completed) {
+        this.completed = completed;
     }
 
     @Override
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/DiskAttribute.java b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/DiskAttribute.java
index 6673ac619cb..bb22afc7ec6 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/DiskAttribute.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/DiskAttribute.java
@@ -242,6 +242,7 @@ public Attribute replace(ByteBuf content) {
                 throw new ChannelException(e);
             }
         }
+        attr.setCompleted(isCompleted());
         return attr;
     }
 
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/DiskFileUpload.java b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/DiskFileUpload.java
index cb52d8814ba..0740a922d2d 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/DiskFileUpload.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/DiskFileUpload.java
@@ -210,6 +210,7 @@ public FileUpload replace(ByteBuf content) {
                 throw new ChannelException(e);
             }
         }
+        upload.setCompleted(isCompleted());
         return upload;
     }
 
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/MemoryAttribute.java b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/MemoryAttribute.java
index ac1db7490b0..25a7bbf32ec 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/MemoryAttribute.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/MemoryAttribute.java
@@ -167,6 +167,7 @@ public Attribute replace(ByteBuf content) {
                 throw new ChannelException(e);
             }
         }
+        attr.setCompleted(isCompleted());
         return attr;
     }
 
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/MemoryFileUpload.java b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/MemoryFileUpload.java
index 06280e39a44..de1cbe25d0c 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/MemoryFileUpload.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/MemoryFileUpload.java
@@ -154,11 +154,11 @@ public FileUpload replace(ByteBuf content) {
         if (content != null) {
             try {
                 upload.setContent(content);
-                return upload;
             } catch (IOException e) {
                 throw new ChannelException(e);
             }
         }
+        upload.setCompleted(isCompleted());
         return upload;
     }
 
diff --git a/codec-http/src/test/java/io/netty/handler/codec/http/multipart/HttpDataTest.java b/codec-http/src/test/java/io/netty/handler/codec/http/multipart/HttpDataTest.java
index 17f90e70fa3..7c8355b5ef5 100644
--- a/codec-http/src/test/java/io/netty/handler/codec/http/multipart/HttpDataTest.java
+++ b/codec-http/src/test/java/io/netty/handler/codec/http/multipart/HttpDataTest.java
@@ -17,6 +17,7 @@
 
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.PooledByteBufAllocator;
+import io.netty.buffer.Unpooled;
 import io.netty.util.CharsetUtil;
 import org.assertj.core.api.ThrowableAssert;
 import org.junit.jupiter.api.BeforeAll;
@@ -68,6 +69,20 @@ void testAddContentEmptyBuffer(HttpData httpData) throws IOException {
         assertThat(content.refCnt()).isEqualTo(0);
     }
 
+    @ParameterizedHttpDataTest
+    void testCompletedFlagPreservedAfterRetainDuplicate(HttpData httpData) throws IOException {
+        httpData.addContent(Unpooled.wrappedBuffer("foo".getBytes(CharsetUtil.UTF_8)), false);
+        assertThat(httpData.isCompleted()).isFalse();
+        HttpData duplicate = httpData.retainedDuplicate();
+        assertThat(duplicate.isCompleted()).isFalse();
+        assertThat(duplicate.release()).isTrue();
+        httpData.addContent(Unpooled.wrappedBuffer("bar".getBytes(CharsetUtil.UTF_8)), true);
+        assertThat(httpData.isCompleted()).isTrue();
+        duplicate = httpData.retainedDuplicate();
+        assertThat(duplicate.isCompleted()).isTrue();
+        assertThat(duplicate.release()).isTrue();
+    }
+
     @Test
     void testAddContentExceedsDefinedSizeDiskFileUpload() {
         doTestAddContentExceedsSize(