diff --git a/websocket-sharp/Server/WebSocketServer.cs b/websocket-sharp/Server/WebSocketServer.cs
index c0a0e2e2..b1b7bf02 100644
--- a/websocket-sharp/Server/WebSocketServer.cs
+++ b/websocket-sharp/Server/WebSocketServer.cs
@@ -766,7 +766,7 @@ namespace WebSocketSharp.Server
       message = null;
 
       if (configuration.ServerCertificate == null) {
-        message = "There is no server certificate for secure connections.";
+        message = "There is no server certificate for secure connection.";
         return false;
       }