diff --git a/tests/storage/__init__.py b/tests/storage/__init__.py
index 5165f9a..3fc283b 100644
--- a/tests/storage/__init__.py
+++ b/tests/storage/__init__.py
@@ -71,7 +71,9 @@ class StorageTests(object):
         assert_item_equals(s.get(href)[0], item)
 
         new_item = self._create_bogus_item()
-        s.update(href, new_item, etag)
+        new_etag = s.update(href, new_item, etag)
+        # See https://github.com/untitaker/vdirsyncer/issues/48
+        assert isinstance(new_etag, (bytes, text_type))
         assert_item_equals(s.get(href)[0], new_item)
 
     def test_update_nonexisting(self):
diff --git a/vdirsyncer/storage/dav.py b/vdirsyncer/storage/dav.py
index e5467e7..9b6782b 100644
--- a/vdirsyncer/storage/dav.py
+++ b/vdirsyncer/storage/dav.py
@@ -217,7 +217,8 @@ class DavStorage(Storage):
         href = self._normalize_href(href)
         if etag is None:
             raise ValueError('etag must be given and must not be None.')
-        return self._put(href, item, etag)
+        href, etag = self._put(href, item, etag)
+        return etag
 
     def upload(self, item):
         href = self._get_href(item)
diff --git a/vdirsyncer/sync.py b/vdirsyncer/sync.py
index b2de7c4..31d7fcf 100644
--- a/vdirsyncer/sync.py
+++ b/vdirsyncer/sync.py
@@ -18,7 +18,7 @@
 import itertools
 
 from . import exceptions, log
-from .utils import iteritems
+from .utils import iteritems, text_type
 sync_logger = log.get(__name__)
 
 
@@ -152,6 +152,7 @@ def action_update(ident, source, dest):
         old_etag = dest_list[dest_href]['etag']
         item = source_list[source_href]['item']
         dest_etag = dest_storage.update(dest_href, item, old_etag)
+        assert isinstance(dest_etag, (bytes, text_type))
 
         source_status = (source_href, source_etag)
         dest_status = (dest_href, dest_etag)