diff --git a/rdflib/namespace.py b/rdflib/namespace.py
index e89b06c28d..bc310167c4 100644
--- a/rdflib/namespace.py
+++ b/rdflib/namespace.py
@@ -142,9 +142,17 @@ def __add__(self, other):
         """Syntactic sugar to allow to write ns[foo] as ns + foo."""
         return self[other]
 
-    def __str__(self):
+    def __unicode__(self):
         return self.__prefix__
 
+    def __bytes__(self):
+        return self.__prefix__.encode('utf-8')
+
+    if PY3:
+        __str__ = __unicode__
+    else:
+        __str__ = __bytes__
+
     def __repr__(self):
         t = type(self)
         return "%s(%r)" % (t.__module__ + '.' + t.__name__, self.__prefix__)