diff --git a/docs/requirements.txt b/docs/requirements.txt
index d1198f0..b9cf1a7 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -17,5 +17,6 @@ sphinxcontrib-jquery
 sphinxcontrib-qthelp
 sphinxcontrib-serializinghtml
 sphinx-reredirects
+sympy
 chardet