diff --git a/doc/rtd-pip-requirements b/doc/rtd-pip-requirements
index 876bcc9b..94484a7c 100644
--- a/doc/rtd-pip-requirements
+++ b/doc/rtd-pip-requirements
@@ -1,3 +1,4 @@
+sphinx>=1.5
 numpy
 matplotlib
 astropy-helpers