diff --git a/docs/requirements.txt b/docs/requirements.txt
index dd723c341ebc..f2330dd94025 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,4 +1,5 @@
 setuptools >= 36.4.0
+sphinx >= 1.6.3
 
 core/
 bigquery/