diff -r eaae4008327d Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Tue Feb 04 09:49:14 2014 +0100
+++ b/Objects/unicodeobject.c	Tue Feb 04 11:02:28 2014 +0000
@@ -9662,7 +9662,7 @@
     PyObject *last_obj;
     unsigned int kind = 0;
 
-    fseq = PySequence_Fast(seq, "");
+    fseq = PySequence_Fast(seq, "can only join an iterable");
     if (fseq == NULL) {
         return NULL;
     }