diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker07.java b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker07.java
index a2fce7c911..91b963271e 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker07.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker07.java
@@ -218,12 +218,19 @@ public class WebSocketClientHandshaker07 extends WebSocketClientHandshaker {
 
         if (customHeaders != null) {
             headers.add(customHeaders);
+            if (!headers.contains(HttpHeaderNames.HOST)) {
+                // Only add HOST header if customHeaders did not contain it.
+                //
+                // See https://github.com/netty/netty/issues/10101
+                headers.set(HttpHeaderNames.HOST, websocketHostValue(wsURL));
+            }
+        } else {
+            headers.set(HttpHeaderNames.HOST, websocketHostValue(wsURL));
         }
 
         headers.set(HttpHeaderNames.UPGRADE, HttpHeaderValues.WEBSOCKET)
                .set(HttpHeaderNames.CONNECTION, HttpHeaderValues.UPGRADE)
-               .set(HttpHeaderNames.SEC_WEBSOCKET_KEY, key)
-               .set(HttpHeaderNames.HOST, websocketHostValue(wsURL));
+               .set(HttpHeaderNames.SEC_WEBSOCKET_KEY, key);
 
         if (!headers.contains(HttpHeaderNames.SEC_WEBSOCKET_ORIGIN)) {
             headers.set(HttpHeaderNames.SEC_WEBSOCKET_ORIGIN, websocketOriginValue(wsURL));
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker08.java b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker08.java
index 245eff8753..76cf9c1874 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker08.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker08.java
@@ -220,12 +220,19 @@ public class WebSocketClientHandshaker08 extends WebSocketClientHandshaker {
 
         if (customHeaders != null) {
             headers.add(customHeaders);
+            if (!headers.contains(HttpHeaderNames.HOST)) {
+                // Only add HOST header if customHeaders did not contain it.
+                //
+                // See https://github.com/netty/netty/issues/10101
+                headers.set(HttpHeaderNames.HOST, websocketHostValue(wsURL));
+            }
+        } else {
+            headers.set(HttpHeaderNames.HOST, websocketHostValue(wsURL));
         }
 
         headers.set(HttpHeaderNames.UPGRADE, HttpHeaderValues.WEBSOCKET)
                .set(HttpHeaderNames.CONNECTION, HttpHeaderValues.UPGRADE)
-               .set(HttpHeaderNames.SEC_WEBSOCKET_KEY, key)
-               .set(HttpHeaderNames.HOST, websocketHostValue(wsURL));
+               .set(HttpHeaderNames.SEC_WEBSOCKET_KEY, key);
 
         if (!headers.contains(HttpHeaderNames.SEC_WEBSOCKET_ORIGIN)) {
             headers.set(HttpHeaderNames.SEC_WEBSOCKET_ORIGIN, websocketOriginValue(wsURL));
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker13.java b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker13.java
index 8efbb4a2e5..82f90b4c8d 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker13.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker13.java
@@ -221,12 +221,19 @@ public class WebSocketClientHandshaker13 extends WebSocketClientHandshaker {
 
         if (customHeaders != null) {
             headers.add(customHeaders);
+            if (!headers.contains(HttpHeaderNames.HOST)) {
+                // Only add HOST header if customHeaders did not contain it.
+                //
+                // See https://github.com/netty/netty/issues/10101
+                headers.set(HttpHeaderNames.HOST, websocketHostValue(wsURL));
+            }
+        } else {
+            headers.set(HttpHeaderNames.HOST, websocketHostValue(wsURL));
         }
 
         headers.set(HttpHeaderNames.UPGRADE, HttpHeaderValues.WEBSOCKET)
                .set(HttpHeaderNames.CONNECTION, HttpHeaderValues.UPGRADE)
-               .set(HttpHeaderNames.SEC_WEBSOCKET_KEY, key)
-               .set(HttpHeaderNames.HOST, websocketHostValue(wsURL));
+               .set(HttpHeaderNames.SEC_WEBSOCKET_KEY, key);
 
         if (!headers.contains(HttpHeaderNames.ORIGIN)) {
             headers.set(HttpHeaderNames.ORIGIN, websocketOriginValue(wsURL));
diff --git a/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker07Test.java b/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker07Test.java
index 4d9be6cb67..dea8b94992 100644
--- a/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker07Test.java
+++ b/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker07Test.java
@@ -15,12 +15,33 @@
  */
 package io.netty.handler.codec.http.websocketx;
 
+import io.netty.handler.codec.http.DefaultHttpHeaders;
+import io.netty.handler.codec.http.FullHttpRequest;
 import io.netty.handler.codec.http.HttpHeaderNames;
 import io.netty.handler.codec.http.HttpHeaders;
+import org.junit.Test;
 
 import java.net.URI;
 
+import static org.junit.Assert.assertEquals;
+
 public class WebSocketClientHandshaker07Test extends WebSocketClientHandshakerTest {
+
+    @Test
+    public void testHostHeaderPreserved() {
+        URI uri = URI.create("ws://localhost:9999");
+        WebSocketClientHandshaker handshaker = newHandshaker(uri, null,
+                new DefaultHttpHeaders().set(HttpHeaderNames.HOST, "test.netty.io"), false);
+
+        FullHttpRequest request = handshaker.newHandshakeRequest();
+        try {
+            assertEquals("/", request.uri());
+            assertEquals("test.netty.io", request.headers().get(HttpHeaderNames.HOST));
+        } finally {
+            request.release();
+        }
+    }
+
     @Override
     protected WebSocketClientHandshaker newHandshaker(URI uri, String subprotocol, HttpHeaders headers,
                                                       boolean absoluteUpgradeUrl) {
diff --git a/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshakerTest.java b/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshakerTest.java
index 327439d678..3abf013c61 100644
--- a/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshakerTest.java
+++ b/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshakerTest.java
@@ -364,7 +364,9 @@ public abstract class WebSocketClientHandshakerTest {
 
         // add values for the headers that are reserved for use in the websockets handshake
         for (CharSequence header : getHandshakeRequiredHeaderNames()) {
-            inputHeaders.add(header, bogusHeaderValue);
+            if (!HttpHeaderNames.HOST.equals(header)) {
+                inputHeaders.add(header, bogusHeaderValue);
+            }
         }
         inputHeaders.add(getProtocolHeaderName(), bogusSubProtocol);