diff --git a/doc/source/requirements.txt b/doc/source/requirements.txt
index 74079111..394ae52a 100644
--- a/doc/source/requirements.txt
+++ b/doc/source/requirements.txt
@@ -3,4 +3,5 @@ scipy
 six
 decorator
 matplotlib
-paramz
\ No newline at end of file
+paramz
+cython
\ No newline at end of file