--- libev/ev.c	2019/12/28 07:37:07	1.519
+++ libev/ev.c	2019/12/28 07:44:15	1.520
@@ -3003,14 +3003,14 @@
 {
   unsigned int flags = 0;
 
-  if (EV_USE_PORT    ) flags |= EVBACKEND_PORT;
-  if (EV_USE_KQUEUE  ) flags |= EVBACKEND_KQUEUE;
-  if (EV_USE_EPOLL   ) flags |= EVBACKEND_EPOLL;
-  if (EV_USE_LINUXAIO) flags |= EVBACKEND_LINUXAIO;
-  if (EV_USE_IOURING ) flags |= EVBACKEND_IOURING;
-  if (EV_USE_POLL    ) flags |= EVBACKEND_POLL;
-  if (EV_USE_SELECT  ) flags |= EVBACKEND_SELECT;
-  
+  if (EV_USE_PORT                                      ) flags |= EVBACKEND_PORT;
+  if (EV_USE_KQUEUE                                    ) flags |= EVBACKEND_KQUEUE;
+  if (EV_USE_EPOLL                                     ) flags |= EVBACKEND_EPOLL;
+  if (EV_USE_LINUXAIO                                  ) flags |= EVBACKEND_LINUXAIO;
+  if (EV_USE_IOURING && ev_linux_version () >= 0x050601) flags |= EVBACKEND_IOURING; /* 5.6.1+ */
+  if (EV_USE_POLL                                      ) flags |= EVBACKEND_POLL;
+  if (EV_USE_SELECT                                    ) flags |= EVBACKEND_SELECT;
+
   return flags;
 }