diff --git a/src/plugins/nat/nat44-ed/nat44_ed_api.c b/src/plugins/nat/nat44-ed/nat44_ed_api.c
index ea29514d729..56e29601f35 100644
--- a/src/plugins/nat/nat44-ed/nat44_ed_api.c
+++ b/src/plugins/nat/nat44-ed/nat44_ed_api.c
@@ -590,7 +590,7 @@ static void
     }
 
   sw_if_index = clib_net_to_host_u32 (mp->external_sw_if_index);
-  if (sw_if_index)
+  if (sw_if_index != ~0)
     {
       flags |= NAT_SM_FLAG_SWITCH_ADDRESS;
     }