diff --git a/requirements.txt b/requirements.txt
index a387142..89fae1f 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,6 +7,7 @@ itsdangerous==0.24
 Jinja2==2.8
 MarkupSafe==0.23
 mimerender==0.5.5
+pyst3==0.4.2
 python-dateutil==2.4.2
 python-mimeparse==0.1.4
 pyzmq==15.1.0