diff --git a/src/calibre/utils/date.py b/src/calibre/utils/date.py
index f3814042d5..90057cd451 100644
--- a/src/calibre/utils/date.py
+++ b/src/calibre/utils/date.py
@@ -194,9 +194,11 @@ def isoformat(date_time, assume_utc=False, as_utc=True, sep='T'):
     # str(sep) because isoformat barfs with unicode sep on python 2.x
     return unicode(date_time.isoformat(str(sep)))
 
+
 def internal_iso_format_string():
     return 'yyyy-MM-ddThh:mm:ss'
 
+
 def w3cdtf(date_time, assume_utc=False):
     if hasattr(date_time, 'tzinfo'):
         if date_time.tzinfo is None: