diff --git a/src/calibre/ebooks/metadata/opf3_test.py b/src/calibre/ebooks/metadata/opf3_test.py
index 258454dae6..8a7ce4ffe0 100644
--- a/src/calibre/ebooks/metadata/opf3_test.py
+++ b/src/calibre/ebooks/metadata/opf3_test.py
@@ -175,11 +175,13 @@ class TestOPF3(unittest.TestCase):
         from calibre.utils.date import utcnow
 
         def rl(root):
-            return read_pubdate(root, read_prefixes(root), read_refines(root)), read_timestamp(root, read_prefixes(root), read_refines(root))
+            p, r = read_prefixes(root), read_refines(root)
+            return read_pubdate(root, p, r), read_timestamp(root, p, r)
 
         def st(root, pd, ts):
-            set_pubdate(root, read_prefixes(root), read_refines(root), pd)
-            set_timestamp(root, read_prefixes(root), read_refines(root), ts)
+            p, r = read_prefixes(root), read_refines(root)
+            set_pubdate(root, p, r, pd)
+            set_timestamp(root, p, r, ts)
             return rl(root)
 
         def ae(root, y1=None, y2=None):
@@ -192,7 +194,8 @@ class TestOPF3(unittest.TestCase):
         root = self.get_opf('''<dc:date>1999-3-2</dc:date><meta property="calibre:timestamp" scheme="dcterms:W3CDTF">2001</meta>''')
         ae(root, 1999, 2001)
         n = utcnow()
-        self.ae(st(root, n, n), (n, n))
+        q = n.replace(microsecond=0)
+        self.ae(st(root, n, n), (n, q))
         root = self.get_opf('''<dc:date>1999-3-2</dc:date><meta name="calibre:timestamp" content="2001-1-1"/>''')
         ae(root, 1999, 2001)
         root = self.get_opf('''<meta property="dcterms:modified">2003</meta>''')
diff --git a/src/calibre/utils/date.py b/src/calibre/utils/date.py
index 2748a0bf01..7a33f0b865 100644
--- a/src/calibre/utils/date.py
+++ b/src/calibre/utils/date.py
@@ -199,7 +199,7 @@ def w3cdtf(date_time, assume_utc=False):
             date_time = date_time.replace(tzinfo=_utc_tz if assume_utc else
                     _local_tz)
         date_time = date_time.astimezone(_utc_tz if as_utc else _local_tz)
-    return unicode(date_time.strftime('%Y-%M-%dT%H:%M:%SZ'))
+    return unicode(date_time.strftime('%Y-%m-%dT%H:%M:%SZ'))
 
 
 def as_local_time(date_time, assume_utc=True):