diff --git a/radicale/__init__.py b/radicale/__init__.py
index ae53c89..f70e58d 100644
--- a/radicale/__init__.py
+++ b/radicale/__init__.py
@@ -842,6 +842,4 @@ class Application:
             headers = {"Content-Type": "text/xml; charset=%s" % self.encoding}
             status, xml_answer = xmlutils.report(
                 base_prefix, path, xml_content, collection)
-            if status == client.PRECONDITION_FAILED:
-                return PRECONDITION_FAILED
             return (status, headers, self._write_xml_content(xml_answer))
diff --git a/radicale/xmlutils.py b/radicale/xmlutils.py
index 68603b9..ff91f82 100644
--- a/radicale/xmlutils.py
+++ b/radicale/xmlutils.py
@@ -127,6 +127,13 @@ def _href(base_prefix, href):
     return quote("%s%s" % (base_prefix, href))
 
 
+def _webdav_error(namespace, name):
+    """Generate XML error message."""
+    root = ET.Element(_tag("D", "error"))
+    root.append(ET.Element(_tag(namespace, name)))
+    return root
+
+
 def _date_to_datetime(date_):
     """Transform a date to a UTC datetime.
 
@@ -1041,7 +1048,8 @@ def report(base_prefix, path, xml_request, collection):
             # Invalid sync token
             collection.logger.warning("Client provided invalid sync token %r: "
                                       "%s", old_sync_token, e, exc_info=True)
-            return client.PRECONDITION_FAILED, None
+            return (client.PRECONDITION_FAILED,
+                    _webdav_error("D", "valid-sync-token"))
         hreferences = ("/" + posixpath.join(collection.path, n) for n in names)
         # Append current sync token to response
         sync_token_element = ET.Element(_tag("D", "sync-token"))