diff --git a/SOPE/NGCards/TimeZones/UPDATING b/SOPE/NGCards/TimeZones/UPDATING
index d8eea9ebc..dd11079fc 100644
--- a/SOPE/NGCards/TimeZones/UPDATING
+++ b/SOPE/NGCards/TimeZones/UPDATING
@@ -11,7 +11,7 @@ To updated the timezone files:
 
 3- run the conversion tool and adjust the PRODID
 
-  vzic --olson-dir /tmp/zones/ --output-dir SOGo/SOPE/NGCards/TimeZones/
+  vzic --pure --olson-dir /tmp/zones/ --output-dir SOGo/SOPE/NGCards/TimeZones/
   cd SOGo/SOPE/NGCards/TimeZones/
   rm -f zones.h zones.tab