diff --git a/websocket-sharp/Net/HttpUtility.cs b/websocket-sharp/Net/HttpUtility.cs
index 584818c5..b859fab3 100644
--- a/websocket-sharp/Net/HttpUtility.cs
+++ b/websocket-sharp/Net/HttpUtility.cs
@@ -1194,8 +1194,11 @@ namespace WebSocketSharp.Net
 
       var len = bytes.Length;
       if (len == 0) {
-        if (offset != 0 || count != 0)
-          throw new ArgumentException ("An empty byte array.", "bytes");
+        if (offset != 0)
+          throw new ArgumentOutOfRangeException ("offset");
+
+        if (count != 0)
+          throw new ArgumentOutOfRangeException ("count");
 
         return bytes;
       }