diff --git a/websocket-sharp/Server/WebSocketSessionManager.cs b/websocket-sharp/Server/WebSocketSessionManager.cs
index f87d3a0d..6dca4079 100644
--- a/websocket-sharp/Server/WebSocketSessionManager.cs
+++ b/websocket-sharp/Server/WebSocketSessionManager.cs
@@ -946,19 +946,66 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Closes the session with the specified <paramref name="id"/>, <paramref name="code"/>,
-    /// and <paramref name="reason"/>.
+    /// Closes the specified session with <paramref name="code"/> and
+    /// <paramref name="reason"/>.
     /// </summary>
     /// <param name="id">
     /// A <see cref="string"/> that represents the ID of the session to close.
     /// </param>
     /// <param name="code">
-    /// One of the <see cref="CloseStatusCode"/> enum values, represents the status code
-    /// indicating the reason for the close.
+    ///   <para>
+    ///   One of the <see cref="CloseStatusCode"/> enum values.
+    ///   </para>
+    ///   <para>
+    ///   It represents the status code indicating the reason for the close.
+    ///   </para>
     /// </param>
     /// <param name="reason">
-    /// A <see cref="string"/> that represents the reason for the close.
+    ///   <para>
+    ///   A <see cref="string"/> that represents the reason for the close.
+    ///   </para>
+    ///   <para>
+    ///   The size must be 123 bytes or less in UTF-8.
+    ///   </para>
     /// </param>
+    /// <exception cref="ArgumentNullException">
+    /// <paramref name="id"/> is <see langword="null"/>.
+    /// </exception>
+    /// <exception cref="ArgumentException">
+    ///   <para>
+    ///   <paramref name="id"/> is an empty string.
+    ///   </para>
+    ///   <para>
+    ///   -or-
+    ///   </para>
+    ///   <para>
+    ///   The session could not be found.
+    ///   </para>
+    ///   <para>
+    ///   -or-
+    ///   </para>
+    ///   <para>
+    ///   <paramref name="code"/> is
+    ///   <see cref="CloseStatusCode.MandatoryExtension"/>.
+    ///   </para>
+    ///   <para>
+    ///   -or-
+    ///   </para>
+    ///   <para>
+    ///   <paramref name="code"/> is
+    ///   <see cref="CloseStatusCode.NoStatus"/> and there is
+    ///   <paramref name="reason"/>.
+    ///   </para>
+    ///   <para>
+    ///   -or-
+    ///   </para>
+    ///   <para>
+    ///   <paramref name="reason"/> could not be UTF-8-encoded.
+    ///   </para>
+    /// </exception>
+    /// <exception cref="ArgumentOutOfRangeException">
+    /// The size of <paramref name="reason"/> is greater than 123 bytes.
+    /// </exception>
     public void CloseSession (string id, CloseStatusCode code, string reason)
     {
       IWebSocketSession session;