diff --git a/Ccs/ccs_function_lib.py b/Ccs/ccs_function_lib.py
index 5f8dbe16c9716d645c2db60b6754bdbdb83e48cf..8ebfaaf07c5272303dd75f408a5425956ab3458e 100644
--- a/Ccs/ccs_function_lib.py
+++ b/Ccs/ccs_function_lib.py
@@ -2466,6 +2466,7 @@ def PUSpack(version=0, typ=0, dhead=0, apid=0, gflags=0b11, sc=0, pktl=0,
         header.bits.SERV_SUB_TYPE = sst
         header.bits.DEST_ID = sdid
         ctime, ftime, sync = calc_timestamp(timestamp)
+        sync = 0 if sync is None else sync
         header.bits.CTIME = ctime
         header.bits.FTIME = ftime
         header.bits.TIMESYNC = sync