diff --git a/SOPE/NGCards/iCalTimeZonePeriod.m b/SOPE/NGCards/iCalTimeZonePeriod.m
index be0d53da3..b7a8b23da 100644
--- a/SOPE/NGCards/iCalTimeZonePeriod.m
+++ b/SOPE/NGCards/iCalTimeZonePeriod.m
@@ -64,6 +64,10 @@
   offsetTo = [[self uniqueChildWithTag: offsetName]
                flattenedValuesForKey: @""];
   length = [offsetTo length];
+
+  if (!length)
+    return seconds;
+
   negative = [offsetTo hasPrefix: @"-"];
   if (negative)
     {