diff --git a/wordfreq/__init__.py b/wordfreq/__init__.py
index afb1971..b10d635 100644
--- a/wordfreq/__init__.py
+++ b/wordfreq/__init__.py
@@ -230,6 +230,7 @@ def word_frequency(word, lang, wordlist='combined', minimum=0.):
       - Full text of Wikipedia
       - A sample of 72 million tweets collected from Twitter in 2014,
         divided roughly into languages using automatic language detection
+      - Google Books Syntactic Ngrams 2013
       - Frequencies extracted from OpenSubtitles
       - The Leeds Internet Corpus
       - Google Books Ngrams and Google Books Syntactic Ngrams