diff --git a/src/calibre/ebooks/mobi/writer.py b/src/calibre/ebooks/mobi/writer.py
index 9332e13ac5..a320bd7691 100644
--- a/src/calibre/ebooks/mobi/writer.py
+++ b/src/calibre/ebooks/mobi/writer.py
@@ -120,7 +120,8 @@ class Serializer(object):
             buffer.write('<reference title="%s" type="%s" '
                          % (ref.title, ref.type))
             self.serialize_href(ref.href)
-            buffer.write('/>')
+            # Space required or won't work, I kid you not
+            buffer.write(' />')
         buffer.write('</guide>')
 
     def serialize_href(self, href, base=None):