diff --git a/lib/spack/docs/requirements.txt b/lib/spack/docs/requirements.txt
index d3fe0d18d7f..bbb32aa55eb 100644
--- a/lib/spack/docs/requirements.txt
+++ b/lib/spack/docs/requirements.txt
@@ -1,5 +1,5 @@
 # These dependencies should be installed using pip in order
 # to build the documentation.
 
-sphinx
+sphinx==1.7.0
 sphinxcontrib-programoutput