diff --git a/backend/net.c.orig b/backend/net.c
index 7c4aae9..0adfbc2 100644
--- a/backend/net.c.orig
+++ b/backend/net.c
@@ -1043,12 +1043,12 @@ sane_init (SANE_Int * version_code, SANE_Auth_Callback authorize)
 	      continue;
 	    }
 #if WITH_AVAHI
-	  avahi_threaded_poll_lock (avahi_thread);
+	  if(avahi_thread) avahi_threaded_poll_lock (avahi_thread);
 #endif /* WITH_AVAHI */
 	  DBG (2, "sane_init: trying to add %s\n", device_name);
 	  add_device (device_name, 0);
 #if WITH_AVAHI
-	  avahi_threaded_poll_unlock (avahi_thread);
+	  if(avahi_thread) avahi_threaded_poll_unlock (avahi_thread);
 #endif /* WITH_AVAHI */
 	}
 
@@ -1094,12 +1094,12 @@ sane_init (SANE_Int * version_code, SANE_Auth_Callback authorize)
 		  continue;
 #endif /* ENABLE_IPV6 */
 #if WITH_AVAHI
-	      avahi_threaded_poll_lock (avahi_thread);
+	      if(avahi_thread) avahi_threaded_poll_lock (avahi_thread);
 #endif /* WITH_AVAHI */
 	      DBG (2, "sane_init: trying to add %s\n", host);
 	      add_device (host, 0);
 #if WITH_AVAHI
-	      avahi_threaded_poll_unlock (avahi_thread);
+	      if(avahi_thread) avahi_threaded_poll_unlock (avahi_thread);
 #endif /* WITH_AVAHI */
 	    }
 	  free (copy);
@@ -1517,11 +1517,11 @@ sane_open (SANE_String_Const full_name, SANE_Handle * meta_handle)
 	   "sane_open: device %s not found, trying to register it anyway\n",
 	   nd_name);
 #if WITH_AVAHI
-      avahi_threaded_poll_lock (avahi_thread);
+      if(avahi_thread) avahi_threaded_poll_lock (avahi_thread);
 #endif /* WITH_AVAHI */
       status = add_device (nd_name, &dev);
 #if WITH_AVAHI
-      avahi_threaded_poll_unlock (avahi_thread);
+      if(avahi_thread) avahi_threaded_poll_unlock (avahi_thread);
 #endif /* WITH_AVAHI */
       if (status != SANE_STATUS_GOOD)
 	{
