diff --git a/ntp_core.c b/ntp_core.c
index 847932b..d67c152 100644
--- a/ntp_core.c
+++ b/ntp_core.c
@@ -373,6 +373,8 @@ do_size_checks(void)
   assert(offsetof(NTP_Packet, originate_ts)    == 24);
   assert(offsetof(NTP_Packet, receive_ts)      == 32);
   assert(offsetof(NTP_Packet, transmit_ts)     == 40);
+
+  assert(sizeof (NTP_EFExpMonoRoot) == 24);
 }
 
 /* ================================================== */