diff --git a/doc/source/requirements.txt b/doc/source/requirements.txt
index 846d6cd6..519048a3 100644
--- a/doc/source/requirements.txt
+++ b/doc/source/requirements.txt
@@ -5,4 +5,5 @@ decorator
 matplotlib
 paramz
 cython
-mock
\ No newline at end of file
+mock
+sympy
\ No newline at end of file