diff --git a/src/calibre/utils/config_base.py b/src/calibre/utils/config_base.py
index b78a14b3e3..8c76f98c4a 100644
--- a/src/calibre/utils/config_base.py
+++ b/src/calibre/utils/config_base.py
@@ -517,7 +517,7 @@ def create_global_prefs(conf_obj=None):
 prefs = ConfigProxy(create_global_prefs())
 if prefs['installation_uuid'] is None:
     import uuid
-    prefs['installation_uuid'] = str(uuid.uuid4())
+    prefs['installation_uuid'] = unicode_type(uuid.uuid4())
 
 # Read tweaks