diff --git a/crates/ruma-client-api/src/r0/uiaa.rs b/crates/ruma-client-api/src/r0/uiaa.rs
index 4b8a24c2..9a42180e 100644
--- a/crates/ruma-client-api/src/r0/uiaa.rs
+++ b/crates/ruma-client-api/src/r0/uiaa.rs
@@ -307,6 +307,7 @@ impl<'a> FallbackAcknowledgement<'a> {
 
 #[doc(hidden)]
 #[derive(Clone, Debug, Serialize)]
+#[non_exhaustive]
 pub struct CustomAuthData<'a> {
     #[serde(rename = "type")]
     pub auth_type: &'a str,
@@ -317,6 +318,7 @@ pub struct CustomAuthData<'a> {
 
 #[doc(hidden)]
 #[derive(Clone, Debug, Deserialize)]
+#[non_exhaustive]
 pub struct IncomingCustomAuthData {
     #[serde(rename = "type")]
     pub auth_type: String,