diff --git a/axum/CHANGELOG.md b/axum/CHANGELOG.md
index 0362b501..75558544 100644
--- a/axum/CHANGELOG.md
+++ b/axum/CHANGELOG.md
@@ -8,8 +8,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 # Unreleased
 
 - **breaking:** Require `Output = ()` on `WebSocketStream::on_upgrade` ([#644])
+- **breaking:** Make `TypedHeaderRejectionReason` `#[non_exhaustive]` ([#665])
 
 [#644]: https://github.com/tokio-rs/axum/pull/644
+[#665]: https://github.com/tokio-rs/axum/pull/665
 
 # 0.4.4 (13. January, 2021)
 
diff --git a/axum/src/extract/typed_header.rs b/axum/src/extract/typed_header.rs
index 0151cfe2..e5a6f99f 100644
--- a/axum/src/extract/typed_header.rs
+++ b/axum/src/extract/typed_header.rs
@@ -98,6 +98,7 @@ impl TypedHeaderRejection {
 
 /// Additional information regarding a [`TypedHeaderRejection`](super::TypedHeaderRejection)
 #[derive(Debug)]
+#[non_exhaustive]
 pub enum TypedHeaderRejectionReason {
     /// The header was missing from the HTTP request
     Missing,