diff --git a/websocket-sharp/AuthenticationChallenge.cs b/websocket-sharp/Net/AuthenticationChallenge.cs
similarity index 98%
rename from websocket-sharp/AuthenticationChallenge.cs
rename to websocket-sharp/Net/AuthenticationChallenge.cs
index d5dc022b..ac39f121 100644
--- a/websocket-sharp/AuthenticationChallenge.cs
+++ b/websocket-sharp/Net/AuthenticationChallenge.cs
@@ -29,9 +29,8 @@
 using System;
 using System.Collections.Specialized;
 using System.Text;
-using WebSocketSharp.Net;
 
-namespace WebSocketSharp
+namespace WebSocketSharp.Net
 {
   internal class AuthenticationChallenge
   {
diff --git a/websocket-sharp/websocket-sharp.csproj b/websocket-sharp/websocket-sharp.csproj
index 372cc227..bcd95cca 100644
--- a/websocket-sharp/websocket-sharp.csproj
+++ b/websocket-sharp/websocket-sharp.csproj
@@ -110,7 +110,6 @@
     <Compile Include="Net\HttpHeaderInfo.cs" />
     <Compile Include="CompressionMethod.cs" />
     <Compile Include="WebSocketException.cs" />
-    <Compile Include="AuthenticationChallenge.cs" />
     <Compile Include="AuthenticationResponse.cs" />
     <Compile Include="LogData.cs" />
     <Compile Include="LogLevel.cs" />
@@ -135,6 +134,7 @@
     <Compile Include="Net\ChunkedRequestStream.cs" />
     <Compile Include="Net\QueryStringCollection.cs" />
     <Compile Include="WebSocketFrame.cs" />
+    <Compile Include="Net\AuthenticationChallenge.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <ItemGroup>