diff --git a/cps/db.py b/cps/db.py
index 1c274baa..7bb4ab7c 100755
--- a/cps/db.py
+++ b/cps/db.py
@@ -280,6 +280,9 @@ class Books(Base):
                                                                  self.timestamp, self.pubdate, self.series_index,
                                                                  self.last_modified, self.path, self.has_cover)
 
+    @property
+    def atom_timestamp(self):
+        return (self.timestamp or '').replace(' ', 'T')
 
 class Custom_Columns(Base):
     __tablename__ = 'custom_columns'
diff --git a/cps/templates/feed.xml b/cps/templates/feed.xml
index fce047d9..ecdb5f54 100644
--- a/cps/templates/feed.xml
+++ b/cps/templates/feed.xml
@@ -38,7 +38,7 @@
   <entry>
     <title>{{entry.title}}</title>
     <id>{{entry.uuid}}</id>
-    <updated>{{entry.timestamp}}</updated>
+    <updated>{{entry.atom_timestamp}}</updated>
     <author>
       <name>{{entry.authors[0].name}}</name>
     </author>
@@ -55,7 +55,7 @@
     {% endif %}
     {% for format in entry.data %}
     <link rel="http://opds-spec.org/acquisition" href="{{ url_for('get_opds_download_link', book_id=entry.id, book_format=format.format|lower)}}"
-          length="{{format.uncompressed_size}}" mtime="{{entry.timestamp}}" type="{{format.format|lower|mimetype}}"/>
+          length="{{format.uncompressed_size}}" mtime="{{entry.atom_timestamp}}" type="{{format.format|lower|mimetype}}"/>
     {% endfor %}
   </entry>
   {% endfor %}