diff --git a/extra/requirements-iso_8601.txt b/extra/requirements-iso_8601.txt
index 59c84ec..03c428b 100644
--- a/extra/requirements-iso_8601.txt
+++ b/extra/requirements-iso_8601.txt
@@ -1 +1 @@
-ciso8601>=2.1
+ciso8601>=2.3.3