diff --git a/ntp_core.c b/ntp_core.c
index bea86a6..8933c49 100644
--- a/ntp_core.c
+++ b/ntp_core.c
@@ -395,7 +395,8 @@ NCR_DestroyInstance(NCR_Instance instance)
     instance->timer_running = 0;
   }
 
-  NIO_CloseClientSocket(instance->local_addr.sock_fd);
+  if (instance->mode == MODE_CLIENT)
+    NIO_CloseClientSocket(instance->local_addr.sock_fd);
 
   /* Free the data structure */
   Free(instance);