diff --git a/axum/src/json.rs b/axum/src/json.rs
index 9fcb53cb..e1d068fa 100644
--- a/axum/src/json.rs
+++ b/axum/src/json.rs
@@ -15,9 +15,16 @@ use std::ops::{Deref, DerefMut};
 /// JSON Extractor / Response.
 ///
 /// When used as an extractor, it can deserialize request bodies into some type that
-/// implements [`serde::Deserialize`]. If the request body cannot be parsed, or it does not contain
-/// the `Content-Type: application/json` header, it will reject the request and return a
-/// `400 Bad Request` response.
+/// implements [`serde::Deserialize`]. The request will be rejected (and a [`JsonRejection`] will
+/// be returned) if:
+///
+/// - The request doesn't have a `Content-Type: application/json` (or similar) header.
+/// - The body doesn't contain syntactically valid JSON.
+/// - The body contains syntactically valid JSON but it couldn't be deserialized into the target
+/// type.
+/// - Buffering the request body fails.
+///
+/// See [`JsonRejection`] for more details.
 ///
 /// # Extractor example
 ///