diff --git a/websocket-sharp/Net/RequestStream.cs b/websocket-sharp/Net/RequestStream.cs
index 0ed6c6ee..40381779 100644
--- a/websocket-sharp/Net/RequestStream.cs
+++ b/websocket-sharp/Net/RequestStream.cs
@@ -125,8 +125,11 @@ namespace WebSocketSharp.Net
       if (buffer == null)
         throw new ArgumentNullException ("buffer");
 
-      if (offset < 0)
-        throw new ArgumentOutOfRangeException ("offset", "A negative value.");
+      if (offset < 0) {
+        var msg = "A negative value.";
+
+        throw new ArgumentOutOfRangeException ("offset", msg);
+      }
 
       if (count < 0)
         throw new ArgumentOutOfRangeException ("count", "A negative value.");