diff --git a/doc/requirements.txt b/doc/requirements.txt
index c833634da..5c76061d5 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -3,6 +3,5 @@ sphinxcontrib-websupport==1.1.0
 m2r==0.2.1
 Sphinx==1.8.4
 commonmark==0.8.1
-commonmark==0.8.1
 recommonmark==0.5.0
 mrkd==0.1.6