diff --git a/histories/models.py b/histories/models.py
index 908884f..a1f2147 100644
--- a/histories/models.py
+++ b/histories/models.py
@@ -43,9 +43,9 @@ class HistoryEntry(models.Model):
     def to_xml(self, xml_root):
         entry = ET.Element('history')
         entry_url = ET.Element('url')
-        entry_url.text = self.search
+        entry_url.text = str(self.search)
         entry_ts = ET.Element('timestamp')
-        entry_ts.text = self.timestamp.timestamp()
+        entry_ts.text = str(self.timestamp.timestamp())
         entry.append(entry_url)
         entry.append(entry_ts)
         xml_root.append(entry)
@@ -125,9 +125,9 @@ class History(models.Model):
             xml_root = ET.Element('root')
 
         hist_node = ET.Element("history", attrib={
-            'start-ts': self.start_ts,
-            'played': 1 if self.played else 0,
-            'user': self.user.pk,
+            'start-ts': str(self.start_ts),
+            'played': '1' if self.played else '0',
+            'user': str(self.user.pk),
         })
         xml_root.append(hist_node)
         for entry in self.historyentry_set.all():