diff --git a/src/Microsoft.AspNet.WebSockets.Protocol/CommonWebSocket.cs b/src/Microsoft.AspNet.WebSockets.Protocol/CommonWebSocket.cs
index 481e5a9393..c6d82a573b 100644
--- a/src/Microsoft.AspNet.WebSockets.Protocol/CommonWebSocket.cs
+++ b/src/Microsoft.AspNet.WebSockets.Protocol/CommonWebSocket.cs
@@ -4,6 +4,7 @@
 using System;
 using System.Diagnostics.Contracts;
 using System.IO;
+using System.Linq;
 using System.Net.WebSockets;
 using System.Text;
 using System.Threading;
@@ -302,6 +303,11 @@ namespace Microsoft.AspNet.WebSockets.Protocol
                 await SendErrorAbortAndThrow(WebSocketCloseStatus.ProtocolError, "Incorrect masking", cancellationToken);
             }
 
+            if (!ValidateOpCode(_frameInProgress.OpCode))
+            {
+                await SendErrorAbortAndThrow(WebSocketCloseStatus.ProtocolError, "Invalid opcode: " + _frameInProgress.OpCode, cancellationToken);
+            }
+
             if (_frameInProgress.IsControlFrame)
             {
                 if (_frameBytesRemaining > 125)
@@ -455,29 +461,6 @@ namespace Microsoft.AspNet.WebSockets.Protocol
             return result;
         }
 
-        private static bool ValidateCloseStatus(WebSocketCloseStatus closeStatus)
-        {
-            if (closeStatus < (WebSocketCloseStatus)1000 || closeStatus >= (WebSocketCloseStatus)5000)
-            {
-                return false;
-            }
-            else if (closeStatus >= (WebSocketCloseStatus)3000)
-            {
-                // 3000-3999 - Reserved for frameworks
-                // 4000-4999 - Reserved for private usage
-                return true;
-            }
-            int[] validCodes = new[] { 1000, 1001, 1002, 1003, 1007, 1008, 1009, 1010, 1011 };
-            foreach (var validCode in validCodes)
-            {
-                if (closeStatus == (WebSocketCloseStatus)validCode)
-                {
-                    return true;
-                }
-            }
-            return false;
-        }
-
         public async override Task CloseAsync(WebSocketCloseStatus closeStatus, string statusDescription, CancellationToken cancellationToken)
         {
             ThrowIfDisposed();
@@ -617,6 +600,34 @@ namespace Microsoft.AspNet.WebSockets.Protocol
             }
         }
 
+        private bool ValidateOpCode(int opCode)
+        {
+            return Constants.OpCodes.ValidOpCodes.Contains(opCode);
+        }
+
+        private static bool ValidateCloseStatus(WebSocketCloseStatus closeStatus)
+        {
+            if (closeStatus < (WebSocketCloseStatus)1000 || closeStatus >= (WebSocketCloseStatus)5000)
+            {
+                return false;
+            }
+            else if (closeStatus >= (WebSocketCloseStatus)3000)
+            {
+                // 3000-3999 - Reserved for frameworks
+                // 4000-4999 - Reserved for private usage
+                return true;
+            }
+            int[] validCodes = new[] { 1000, 1001, 1002, 1003, 1007, 1008, 1009, 1010, 1011 };
+            foreach (var validCode in validCodes)
+            {
+                if (closeStatus == (WebSocketCloseStatus)validCode)
+                {
+                    return true;
+                }
+            }
+            return false;
+        }
+
         private async Task SendErrorAbortAndThrow(WebSocketCloseStatus error, string message, CancellationToken cancellationToken)
         {
             if (State == WebSocketState.Open || State == WebSocketState.CloseReceived)
diff --git a/src/Microsoft.AspNet.WebSockets.Protocol/Constants.cs b/src/Microsoft.AspNet.WebSockets.Protocol/Constants.cs
index 07756e49e3..60a9340b67 100644
--- a/src/Microsoft.AspNet.WebSockets.Protocol/Constants.cs
+++ b/src/Microsoft.AspNet.WebSockets.Protocol/Constants.cs
@@ -25,7 +25,17 @@ namespace Microsoft.AspNet.WebSockets.Protocol
             public const int BinaryFrame = 0x2;
             public const int CloseFrame = 0x8;
             public const int PingFrame = 0x9;
-            public const int PongFrame = 0xA;            
+            public const int PongFrame = 0xA;
+
+            internal static readonly int[] ValidOpCodes = new int[]
+            {
+                ContinuationFrame,
+                TextFrame,
+                BinaryFrame,
+                CloseFrame,
+                PingFrame,
+                PongFrame,
+            };
         }
     }
 }