From 525216d95714873e5c6e28cd39c66d62a02bd3ca Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sat, 18 Jun 2016 09:41:37 +0530
Subject: [PATCH] ...

---
 src/calibre/ebooks/metadata/utils.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/calibre/ebooks/metadata/utils.py b/src/calibre/ebooks/metadata/utils.py
index 17889cce3b..4645d24cc4 100644
--- a/src/calibre/ebooks/metadata/utils.py
+++ b/src/calibre/ebooks/metadata/utils.py
@@ -70,8 +70,10 @@ def normalize_languages(opf_languages, mi_languages):
 
 def ensure_unique(template, existing):
     b, e = template.rpartition('.')[::2]
-    if e:
+    if b and e:
         e = '.' + e
+    else:
+        b, e = template, ''
     q = template
     c = 0
     while q in existing: