diff --git a/gensim/corpora/ucicorpus.py b/gensim/corpora/ucicorpus.py
index a8911ee07f..6bff230c01 100644
--- a/gensim/corpora/ucicorpus.py
+++ b/gensim/corpora/ucicorpus.py
@@ -207,7 +207,7 @@ def save_corpus(fname, corpus, id2word=None, progress_cnt=10000, metadata=False)
             id2word = utils.dict_from_corpus(corpus)
             num_terms = len(id2word)
         else:
-            num_terms = 1 + max([-1] + id2word.keys())
+            num_terms = 1 + max([-1] + list(id2word))
 
         # write out vocabulary
         fname_vocab = utils.smart_extension(fname, '.vocab')