diff --git a/src/calibre/utils/complete.py b/src/calibre/utils/complete.py
index d688033fce..2f3ec79695 100644
--- a/src/calibre/utils/complete.py
+++ b/src/calibre/utils/complete.py
@@ -117,7 +117,7 @@ class EbookConvert(object):
         self.previous = words[-2 if prefix else -1]
         from calibre.utils.serialize import msgpack_loads
         self.cache = msgpack_loads(open(os.path.join(sys.resources_location,
-            'ebook-convert-complete.calibre_msgpack'), 'rb').read())
+            'ebook-convert-complete.calibre_msgpack'), 'rb').read(), use_list=False)
         self.complete(wc)
 
     def complete(self, wc):
diff --git a/src/calibre/utils/serialize.py b/src/calibre/utils/serialize.py
index d54d6d6885..f5d560c468 100644
--- a/src/calibre/utils/serialize.py
+++ b/src/calibre/utils/serialize.py
@@ -107,9 +107,10 @@ def msgpack_decoder(code, data):
     return decoders[code](msgpack_loads(data), False)
 
 
-def msgpack_loads(dump):
+def msgpack_loads(dump, use_list=True):
+    # use_list controls whether msgpack arrays are unpacked as lists or tuples
     import msgpack
-    return msgpack.unpackb(dump, ext_hook=msgpack_decoder, raw=False)
+    return msgpack.unpackb(dump, ext_hook=msgpack_decoder, raw=False, use_list=use_list)
 
 
 def json_loads(data):