diff --git a/src/apps/sntp/sntp.c b/src/apps/sntp/sntp.c
index 0b5a5ae6..edbeff1a 100644
--- a/src/apps/sntp/sntp.c
+++ b/src/apps/sntp/sntp.c
@@ -318,6 +318,7 @@ sntp_process(const struct sntp_timestamps *timestamps)
 #endif /* SNTP_COMP_ROUNDTRIP */
 
   SNTP_SET_SYSTEM_TIME_NTP(sec, frac);
+  LWIP_UNUSED_ARG(frac); /* might be unused if only seconds are set */
   LWIP_DEBUGF(SNTP_DEBUG_TRACE, ("sntp_process: %s, %" U32_F " us\n",
                                  sntp_format_time(sec), SNTP_FRAC_TO_US(frac)));
 }