diff --git a/websocket-sharp/Server/WebSocketSessionManager.cs b/websocket-sharp/Server/WebSocketSessionManager.cs
index 67a10f8a..b412350e 100644
--- a/websocket-sharp/Server/WebSocketSessionManager.cs
+++ b/websocket-sharp/Server/WebSocketSessionManager.cs
@@ -116,7 +116,7 @@ namespace WebSocketSharp.Server
     /// </value>
     public IEnumerable<string> ActiveIDs {
       get {
-        foreach (var res in broadping (WebSocketFrame.EmptyPingBytes)) {
+        foreach (var res in broadping (_emptyPingFrameAsBytes)) {
           if (res.Value)
             yield return res.Key;
         }