diff --git a/requirements.txt b/requirements.txt
index 4d451d5..28af493 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -14,3 +14,4 @@ django-babel>=0.5.1 # BSD
 django-compressor>=2.0 # MIT
 django-pyscss>=2.0.2 # BSD License (2 clause)
 python-karborclient>=0.6.0 # Apache-2.0
+icalendar>=4.0.2 # BSD