diff --git a/src/weekday.rs b/src/weekday.rs
index bebdd116..bd30e193 100644
--- a/src/weekday.rs
+++ b/src/weekday.rs
@@ -11,6 +11,7 @@ use rkyv::{Archive, Deserialize, Serialize};
 #[derive(PartialEq, Eq, Copy, Clone, Debug, Hash)]
 #[cfg_attr(feature = "rustc-serialize", derive(RustcEncodable, RustcDecodable))]
 #[cfg_attr(feature = "rkyv", derive(Archive, Deserialize, Serialize))]
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 pub enum Weekday {
     /// Monday.
     Mon = 0,