diff --git a/crates/ruma-common/src/events/room/join_rules.rs b/crates/ruma-common/src/events/room/join_rules.rs
index c549d845..fefe7f3b 100644
--- a/crates/ruma-common/src/events/room/join_rules.rs
+++ b/crates/ruma-common/src/events/room/join_rules.rs
@@ -109,6 +109,7 @@ impl<'de> Deserialize<'de> for JoinRule {
 
         #[derive(Deserialize)]
         struct ExtractType<'a> {
+            #[serde(borrow)]
             join_rule: Option<Cow<'a, str>>,
         }