diff --git a/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthRequest.java b/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthRequest.java
index a243d3bd79..28e70ac3d0 100644
--- a/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthRequest.java
+++ b/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthRequest.java
@@ -28,6 +28,7 @@ import java.nio.charset.CharsetEncoder;
  */
 public final class SocksAuthRequest extends SocksRequest {
     private static final CharsetEncoder asciiEncoder = CharsetUtil.getEncoder(CharsetUtil.US_ASCII);
+    private static final SubnegotiationVersion SUBNEGOTIATION_VERSION = SubnegotiationVersion.AUTH_PASSWORD;
     private final String username;
     private final String password;
 
@@ -73,7 +74,7 @@ public final class SocksAuthRequest extends SocksRequest {
 
     @Override
     public void encodeAsByteBuf(ByteBuf byteBuf) {
-        byteBuf.writeByte(getProtocolVersion().getByteValue());
+        byteBuf.writeByte(SUBNEGOTIATION_VERSION.getByteValue());
         byteBuf.writeByte(username.length());
         byteBuf.writeBytes(username.getBytes(CharsetUtil.US_ASCII));
         byteBuf.writeByte(password.length());
diff --git a/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthRequestDecoder.java b/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthRequestDecoder.java
index 79962f640e..3f4e9e8df7 100644
--- a/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthRequestDecoder.java
+++ b/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthRequestDecoder.java
@@ -31,7 +31,7 @@ public class SocksAuthRequestDecoder extends ReplayingDecoder<SocksRequest, Sock
         return name;
     }
 
-    private SocksMessage.ProtocolVersion version;
+    private SocksMessage.SubnegotiationVersion version;
     private int fieldLength;
     private String username;
     private String password;
@@ -45,8 +45,8 @@ public class SocksAuthRequestDecoder extends ReplayingDecoder<SocksRequest, Sock
     public SocksRequest decode(ChannelHandlerContext ctx, ByteBuf byteBuf) throws Exception {
         switch (state()) {
             case CHECK_PROTOCOL_VERSION: {
-                version = SocksMessage.ProtocolVersion.fromByte(byteBuf.readByte());
-                if (version != SocksMessage.ProtocolVersion.SOCKS5) {
+                version = SocksMessage.SubnegotiationVersion.fromByte(byteBuf.readByte());
+                if (version != SocksMessage.SubnegotiationVersion.AUTH_PASSWORD) {
                     break;
                 }
                 checkpoint(State.READ_USERNAME);
diff --git a/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthResponse.java b/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthResponse.java
index 1515e87f76..59a1bd615d 100644
--- a/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthResponse.java
+++ b/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthResponse.java
@@ -24,7 +24,7 @@ import io.netty.buffer.ByteBuf;
  * @see SocksAuthResponseDecoder
  */
 public final class SocksAuthResponse extends SocksResponse {
-
+    private static final SubnegotiationVersion SUBNEGOTIATION_VERSION = SubnegotiationVersion.AUTH_PASSWORD;
     private final AuthStatus authStatus;
 
     /**
@@ -52,7 +52,7 @@ public final class SocksAuthResponse extends SocksResponse {
 
     @Override
     public void encodeAsByteBuf(ByteBuf byteBuf) {
-        byteBuf.writeByte(getProtocolVersion().getByteValue());
+        byteBuf.writeByte(SUBNEGOTIATION_VERSION.getByteValue());
         byteBuf.writeByte(authStatus.getByteValue());
     }
 }
diff --git a/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthResponseDecoder.java b/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthResponseDecoder.java
index 754770d03e..32b176de6a 100644
--- a/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthResponseDecoder.java
+++ b/codec-socks/src/main/java/io/netty/codec/socks/SocksAuthResponseDecoder.java
@@ -30,7 +30,7 @@ public class SocksAuthResponseDecoder extends ReplayingDecoder<SocksResponse, So
         return name;
     }
 
-    private SocksMessage.ProtocolVersion version;
+    private SocksMessage.SubnegotiationVersion version;
     private SocksMessage.AuthStatus authStatus;
     private SocksResponse msg = SocksCommonUtils.UNKNOWN_SOCKS_RESPONSE;
 
@@ -42,8 +42,8 @@ public class SocksAuthResponseDecoder extends ReplayingDecoder<SocksResponse, So
     public SocksResponse decode(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf) throws Exception {
         switch (state()) {
             case CHECK_PROTOCOL_VERSION: {
-                version = SocksMessage.ProtocolVersion.fromByte(byteBuf.readByte());
-                if (version != SocksMessage.ProtocolVersion.SOCKS5) {
+                version = SocksMessage.SubnegotiationVersion.fromByte(byteBuf.readByte());
+                if (version != SocksMessage.SubnegotiationVersion.AUTH_PASSWORD) {
                     break;
                 }
                 checkpoint(State.READ_AUTH_RESPONSE);
diff --git a/codec-socks/src/main/java/io/netty/codec/socks/SocksMessage.java b/codec-socks/src/main/java/io/netty/codec/socks/SocksMessage.java
index c4805eb49b..46e515e183 100644
--- a/codec-socks/src/main/java/io/netty/codec/socks/SocksMessage.java
+++ b/codec-socks/src/main/java/io/netty/codec/socks/SocksMessage.java
@@ -210,6 +210,30 @@ public abstract class SocksMessage {
         }
     }
 
+    public enum SubnegotiationVersion {
+        AUTH_PASSWORD((byte) 0x01),
+        UNKNOWN((byte) 0xff);
+
+        private final byte b;
+
+        private SubnegotiationVersion(byte b) {
+            this.b = b;
+        }
+
+        public static SubnegotiationVersion fromByte(byte b) {
+            for (SubnegotiationVersion code : values()) {
+                if (code.b == b) {
+                    return code;
+                }
+            }
+            return UNKNOWN;
+        }
+
+        public byte getByteValue() {
+            return b;
+        }
+    }
+
     /**
      * Returns the {@link ProtocolVersion} of this {@link SocksMessage}
      *