diff --git a/merge.py b/merge.py
index 0bb759f7..a22e56d0 100755
--- a/merge.py
+++ b/merge.py
@@ -1182,8 +1182,10 @@ def TruncatePeriod(service_period, start, end):
         start: The start date as a string in YYYYMMDD format.
         end: The end date as a string in YYYYMMDD format.
       """
-      service_period.start_date = max(service_period.start_date, start)
-      service_period.end_date = min(service_period.end_date, end)
+      if service_period.start_date is not None:
+        service_period.start_date = max(service_period.start_date, start)
+      if service_period.end_date is not None:
+        service_period.end_date = min(service_period.end_date, end)
       dates_to_delete = []
       for k in service_period.date_exceptions:
         if (k < start) or (k > end):
@@ -1200,7 +1202,7 @@ def TruncatePeriod(service_period, start, end):
     before = (cutoff_date - one_day_delta).strftime('%Y%m%d')
 
     for a in self.feed_merger.a_schedule.GetServicePeriodList():
-      TruncatePeriod(a, 0, before)
+      TruncatePeriod(a, '0'*8, before)
     for b in self.feed_merger.b_schedule.GetServicePeriodList():
       TruncatePeriod(b, cutoff, '9'*8)
 
diff --git a/tests/data/good_feed/calendar.txt b/tests/data/good_feed/calendar.txt
index 0da4c8ff..cac4aea1 100644
--- a/tests/data/good_feed/calendar.txt
+++ b/tests/data/good_feed/calendar.txt
@@ -1,3 +1,3 @@
 service_id,monday,tuesday,wednesday,thursday,friday,saturday,sunday,start_date,end_date
-FULLW,1,1,1,1,1,1,1,20070101,20151231
-WE,0,0,0,0,0,1,1,20070101,20151231
+FULLW,1,1,1,1,1,1,1,20070101,20251231
+WE,0,0,0,0,0,1,1,20070101,20251231
diff --git a/tests/data/googletransit/good_feed/calendar.txt b/tests/data/googletransit/good_feed/calendar.txt
index 0da4c8ff..cac4aea1 100644
--- a/tests/data/googletransit/good_feed/calendar.txt
+++ b/tests/data/googletransit/good_feed/calendar.txt
@@ -1,3 +1,3 @@
 service_id,monday,tuesday,wednesday,thursday,friday,saturday,sunday,start_date,end_date
-FULLW,1,1,1,1,1,1,1,20070101,20151231
-WE,0,0,0,0,0,1,1,20070101,20151231
+FULLW,1,1,1,1,1,1,1,20070101,20251231
+WE,0,0,0,0,0,1,1,20070101,20251231