diff --git a/docs/requirements.txt b/docs/requirements.txt
index 919b855..1e79954 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -4,7 +4,7 @@ networkx
 git+https://github.com/KarrLab/obj_model.git#egg=obj_model
 robpol86-sphinxcontrib-googleanalytics
 six
-Sphinx
+Sphinx >= 1.6
 sphinx_rtd_theme
 sphinxcontrib-bibtex
 sphinxcontrib-spelling; python_version >= '3.0'