diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 0c3d107..0e4b2b3 100755
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -1,6 +1,10 @@
 Changelog
 =========
 
+Unreleased
+------------------------
+- Enh #69: Add `requirements.php`
+
 1.4.2 (January 19, 2023)
 -----------------------
 - Enh #57: Tests for `next` version
diff --git a/requirements.php b/requirements.php
new file mode 100644
index 0000000..e614409
--- /dev/null
+++ b/requirements.php
@@ -0,0 +1,7 @@
+<?php
+
+if (!Yii::$app->getModule('calendar')) {
+    return 'You must first install and enable the Calendar module.';
+}
+
+return null;