diff --git a/requirements.txt b/requirements.txt
index 5b124545..b3b7bcda 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -13,7 +13,7 @@ django-toolbelt==0.0.1
 premailer==3.1.1
 django-widget-tweaks==1.4.1
 gunicorn==19.7.1
-icalendar==4.0
+icalendar==4.0.0
 lxml==4.1.1
 Markdown==2.6.9
 Pillow==4.3.0