diff --git a/openstack/common/timeutils.py b/openstack/common/timeutils.py
index e518733dd..0f346087f 100644
--- a/openstack/common/timeutils.py
+++ b/openstack/common/timeutils.py
@@ -71,14 +71,14 @@ def normalize_time(timestamp):
 
 def is_older_than(before, seconds):
     """Return True if before is older than seconds."""
-    if isinstance(before, str):
+    if isinstance(before, basestring):
         before = parse_strtime(before).replace(tzinfo=None)
     return utcnow() - before > datetime.timedelta(seconds=seconds)
 
 
 def is_newer_than(after, seconds):
     """Return True if after is newer than seconds."""
-    if isinstance(after, str):
+    if isinstance(after, basestring):
         after = parse_strtime(after).replace(tzinfo=None)
     return after - utcnow() > datetime.timedelta(seconds=seconds)