diff --git a/crans_utils.py b/crans_utils.py
index fb3e991..36a7975 100644
--- a/crans_utils.py
+++ b/crans_utils.py
@@ -349,8 +349,7 @@ def datetime_from_generalized_time_format(gtf):
         date, tz = gtf[0:14], gtf[14:]
     else:
         date = gtf.replace("Z", '')
-        tz = '0000'
-    tz = tz.replace('+', '')
+        tz = '+0000'
     the_date = datetime.datetime.strptime(date, "%Y%m%d%H%M%S")
     if pytz is not None:
         tz_dict = build_tz_dict()
@@ -360,10 +359,10 @@ def datetime_from_generalized_time_format(gtf):
 
 def datetime_to_generalized_time_format(datetime_obj):
     """Transforms a datetime to a GTF"""
+    to_append = ""
     if datetime_obj.utcoffset() is None:
         if pytz is not None:
             datetime_obj = pytz.utc.localize(datetime_obj)
-            to_append = ""
         else:
             to_append = "Z"
     mostly_gtf = datetime.datetime.strftime(datetime_obj, "%Y%m%d%H%M%S%z")
@@ -383,9 +382,7 @@ def build_tz_dict():
         d = datetime.datetime.now(mytz).utcoffset().total_seconds()
         hours = int(d)/3600
         minutes = int(float(int(d) % 3600)/60)
-        fmt = "%s%02d%02d" % (sgn(hours), abs(hours), minutes)
+        fmt = "%+03d%02d" % (hours, minutes)
         if fmt not in tz_dict:
             tz_dict[fmt] = mytz
     return tz_dict
-
-sgn = lambda x: '-' if x < 0 else ''