diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketClientExtensionHandler.java b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketClientExtensionHandler.java
index 47073a7b23..165c1cdfc8 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketClientExtensionHandler.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketClientExtensionHandler.java
@@ -63,15 +63,14 @@ public class WebSocketClientExtensionHandler extends ChannelDuplexHandler {
         if (msg instanceof HttpRequest && WebSocketExtensionUtil.isWebsocketUpgrade(((HttpRequest) msg).headers())) {
             HttpRequest request = (HttpRequest) msg;
             String headerValue = request.headers().getAsString(HttpHeaderNames.SEC_WEBSOCKET_EXTENSIONS);
-            List<WebSocketExtensionData> extraExtensions =
-              new ArrayList<WebSocketExtensionData>(extensionHandshakers.size());
-            for (WebSocketClientExtensionHandshaker extensionHandshaker : extensionHandshakers) {
-                extraExtensions.add(extensionHandshaker.newRequestData());
-            }
-            String newHeaderValue = WebSocketExtensionUtil
-              .computeMergeExtensionsHeaderValue(headerValue, extraExtensions);
 
-            request.headers().set(HttpHeaderNames.SEC_WEBSOCKET_EXTENSIONS, newHeaderValue);
+            for (WebSocketClientExtensionHandshaker extensionHandshaker : extensionHandshakers) {
+                WebSocketExtensionData extensionData = extensionHandshaker.newRequestData();
+                headerValue = WebSocketExtensionUtil.appendExtension(headerValue,
+                        extensionData.name(), extensionData.parameters());
+            }
+
+            request.headers().set(HttpHeaderNames.SEC_WEBSOCKET_EXTENSIONS, headerValue);
         }
 
         super.write(ctx, msg, promise);
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketExtensionUtil.java b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketExtensionUtil.java
index 01f1c0036c..567e49e6bf 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketExtensionUtil.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketExtensionUtil.java
@@ -72,53 +72,25 @@ public final class WebSocketExtensionUtil {
         }
     }
 
-    static String computeMergeExtensionsHeaderValue(String userDefinedHeaderValue,
-                                                    List<WebSocketExtensionData> extraExtensions) {
-        List<WebSocketExtensionData> userDefinedExtensions =
-          userDefinedHeaderValue != null ?
-            extractExtensions(userDefinedHeaderValue) :
-            Collections.<WebSocketExtensionData>emptyList();
+    static String appendExtension(String currentHeaderValue, String extensionName,
+            Map<String, String> extensionParameters) {
 
-        for (WebSocketExtensionData userDefined: userDefinedExtensions) {
-            WebSocketExtensionData matchingExtra = null;
-            int i;
-            for (i = 0; i < extraExtensions.size(); i ++) {
-                WebSocketExtensionData extra = extraExtensions.get(i);
-                if (extra.name().equals(userDefined.name())) {
-                    matchingExtra = extra;
-                    break;
-                }
-            }
-            if (matchingExtra == null) {
-                extraExtensions.add(userDefined);
-            } else {
-                // merge with higher precedence to user defined parameters
-                Map<String, String> mergedParameters = new HashMap<String, String>(matchingExtra.parameters());
-                mergedParameters.putAll(userDefined.parameters());
-                extraExtensions.set(i, new WebSocketExtensionData(matchingExtra.name(), mergedParameters));
+        StringBuilder newHeaderValue = new StringBuilder(
+                currentHeaderValue != null ? currentHeaderValue.length() : extensionName.length() + 1);
+        if (currentHeaderValue != null && !currentHeaderValue.trim().isEmpty()) {
+            newHeaderValue.append(currentHeaderValue);
+            newHeaderValue.append(EXTENSION_SEPARATOR);
+        }
+        newHeaderValue.append(extensionName);
+        for (Entry<String, String> extensionParameter : extensionParameters.entrySet()) {
+            newHeaderValue.append(PARAMETER_SEPARATOR);
+            newHeaderValue.append(extensionParameter.getKey());
+            if (extensionParameter.getValue() != null) {
+                newHeaderValue.append(PARAMETER_EQUAL);
+                newHeaderValue.append(extensionParameter.getValue());
             }
         }
-
-        StringBuilder sb = new StringBuilder(150);
-
-        for (WebSocketExtensionData data: extraExtensions) {
-            sb.append(data.name());
-            for (Entry<String, String> parameter : data.parameters().entrySet()) {
-                sb.append(PARAMETER_SEPARATOR);
-                sb.append(parameter.getKey());
-                if (parameter.getValue() != null) {
-                    sb.append(PARAMETER_EQUAL);
-                    sb.append(parameter.getValue());
-                }
-            }
-            sb.append(EXTENSION_SEPARATOR);
-        }
-
-        if (!extraExtensions.isEmpty()) {
-            sb.setLength(sb.length() - EXTENSION_SEPARATOR.length());
-        }
-
-        return sb.toString();
+        return newHeaderValue.toString();
     }
 
     private WebSocketExtensionUtil() {
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketServerExtensionHandler.java b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketServerExtensionHandler.java
index e00090bb79..9e45bcfa63 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketServerExtensionHandler.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketServerExtensionHandler.java
@@ -124,13 +124,13 @@ public class WebSocketServerExtensionHandler extends ChannelDuplexHandler {
 
             if (validExtensions != null) {
                 String headerValue = headers.getAsString(HttpHeaderNames.SEC_WEBSOCKET_EXTENSIONS);
-                List<WebSocketExtensionData> extraExtensions =
-                  new ArrayList<WebSocketExtensionData>(extensionHandshakers.size());
+
                 for (WebSocketServerExtension extension : validExtensions) {
-                    extraExtensions.add(extension.newReponseData());
+                    WebSocketExtensionData extensionData = extension.newReponseData();
+                    headerValue = WebSocketExtensionUtil.appendExtension(headerValue,
+                        extensionData.name(),
+                        extensionData.parameters());
                 }
-                String newHeaderValue = WebSocketExtensionUtil
-                  .computeMergeExtensionsHeaderValue(headerValue, extraExtensions);
                 promise.addListener(new ChannelFutureListener() {
                     @Override
                     public void operationComplete(ChannelFuture future) {
@@ -148,7 +148,7 @@ public class WebSocketServerExtensionHandler extends ChannelDuplexHandler {
                 });
 
                 if (headerValue != null) {
-                    headers.set(HttpHeaderNames.SEC_WEBSOCKET_EXTENSIONS, newHeaderValue);
+                    headers.set(HttpHeaderNames.SEC_WEBSOCKET_EXTENSIONS, headerValue);
                 }
             }
 
diff --git a/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketExtensionUtilTest.java b/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketExtensionUtilTest.java
index eab3b3ba46..12aa06ed66 100644
--- a/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketExtensionUtilTest.java
+++ b/codec-http/src/test/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketExtensionUtilTest.java
@@ -21,63 +21,19 @@ import io.netty.handler.codec.http.HttpHeaderValues;
 import io.netty.handler.codec.http.HttpHeaders;
 import org.junit.Test;
 
-import java.util.List;
-
 import static org.junit.Assert.*;
-import static io.netty.handler.codec.http.websocketx.extensions.WebSocketExtensionUtil.*;
 
 public class WebSocketExtensionUtilTest {
 
     @Test
     public void testIsWebsocketUpgrade() {
         HttpHeaders headers = new DefaultHttpHeaders();
-        assertFalse(isWebsocketUpgrade(headers));
+        assertFalse(WebSocketExtensionUtil.isWebsocketUpgrade(headers));
 
         headers.add(HttpHeaderNames.UPGRADE, HttpHeaderValues.WEBSOCKET);
-        assertFalse(isWebsocketUpgrade(headers));
+        assertFalse(WebSocketExtensionUtil.isWebsocketUpgrade(headers));
 
         headers.add(HttpHeaderNames.CONNECTION, "Keep-Alive, Upgrade");
-        assertTrue(isWebsocketUpgrade(headers));
-    }
-
-    @Test
-    public void computeMergeExtensionsHeaderValueWhenNoUserDefinedHeader() {
-        List<WebSocketExtensionData> extras = extractExtensions("permessage-deflate; client_max_window_bits," +
-          "permessage-deflate; client_no_context_takeover; client_max_window_bits," +
-          "deflate-frame," +
-          "x-webkit-deflate-frame");
-        String newHeaderValue = computeMergeExtensionsHeaderValue(null, extras);
-        assertEquals("permessage-deflate;client_max_window_bits," +
-          "permessage-deflate;client_no_context_takeover;client_max_window_bits," +
-          "deflate-frame," +
-          "x-webkit-deflate-frame", newHeaderValue);
-    }
-
-    @Test
-    public void computeMergeExtensionsHeaderValueWhenNoConflictingUserDefinedHeader() {
-        List<WebSocketExtensionData> extras = extractExtensions("permessage-deflate; client_max_window_bits," +
-          "permessage-deflate; client_no_context_takeover; client_max_window_bits," +
-          "deflate-frame," +
-          "x-webkit-deflate-frame");
-        String newHeaderValue = computeMergeExtensionsHeaderValue("foo, bar", extras);
-        assertEquals("permessage-deflate;client_max_window_bits," +
-          "permessage-deflate;client_no_context_takeover;client_max_window_bits," +
-          "deflate-frame," +
-          "x-webkit-deflate-frame," +
-          "foo," +
-          "bar", newHeaderValue);
-    }
-
-    @Test
-    public void computeMergeExtensionsHeaderValueWhenConflictingUserDefinedHeader() {
-        List<WebSocketExtensionData> extras = extractExtensions("permessage-deflate; client_max_window_bits," +
-          "permessage-deflate; client_no_context_takeover; client_max_window_bits," +
-          "deflate-frame," +
-          "x-webkit-deflate-frame");
-        String newHeaderValue = computeMergeExtensionsHeaderValue("permessage-deflate; client_max_window_bits", extras);
-        assertEquals("permessage-deflate;client_max_window_bits," +
-          "permessage-deflate;client_no_context_takeover;client_max_window_bits," +
-          "deflate-frame," +
-          "x-webkit-deflate-frame", newHeaderValue);
+        assertTrue(WebSocketExtensionUtil.isWebsocketUpgrade(headers));
     }
 }