diff --git a/setup.py b/setup.py
index 74afcda..840da7e 100644
--- a/setup.py
+++ b/setup.py
@@ -36,7 +36,7 @@ setup(
         "console_scripts": ['tm-calendarsync = twomartens.calendarsync.calendarsync:main']
     },
     python_requires="~=3.6",
-    install_requires=[""],
+    install_requires=["ics>=0.4"],
     license="Apache License 2.0",
     classifiers=[
         "Operating System :: OS Independent",