diff --git a/setup.py b/setup.py
index cd5a6e9..c9b3087 100644
--- a/setup.py
+++ b/setup.py
@@ -56,6 +56,7 @@ with open(PACKAGE_NAME + '/_version.py') as f:
 
 REQUIREMENTS_MAIN = [
     'GitPython',
+    'icalendar',
 ]
 REQUIREMENTS_TEST = [
     'pytest',