diff --git a/pyproject.toml b/pyproject.toml
index 850c5006..d7cb6f74 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -61,7 +61,7 @@ optional-dependencies.bench = [
   "py-cpuinfo",
 ]
 optional-dependencies.calendar = [
-  "caldav==1.3.6",
+  "caldav==1.3.9",
 ]
 optional-dependencies.dev = [
   "nc-py-api[bench,calendar,dev-min]",