diff --git a/core/http/Cargo.toml b/core/http/Cargo.toml
index 1c0afafc..033b1f8a 100644
--- a/core/http/Cargo.toml
+++ b/core/http/Cargo.toml
@@ -36,7 +36,7 @@ memchr = "2"
 stable-pattern = "0.1"
 cookie = { version = "0.18", features = ["percent-encode"] }
 state = "0.6"
-transient = { version = "0.3" }
+transient = { version = "0.4" }
 
 [dependencies.serde]
 version = "1.0"
diff --git a/core/lib/Cargo.toml b/core/lib/Cargo.toml
index 9853f654..a1eb28d3 100644
--- a/core/lib/Cargo.toml
+++ b/core/lib/Cargo.toml
@@ -29,7 +29,7 @@ http3-preview = ["s2n-quic", "s2n-quic-h3", "tls"]
 secrets = ["cookie/private", "cookie/key-expansion"]
 json = ["serde_json"]
 msgpack = ["rmp-serde"]
-uuid = ["uuid_", "rocket_http/uuid"]
+uuid = ["uuid_", "rocket_http/uuid", "transient/uuid"]
 tls = ["rustls", "tokio-rustls", "rustls-pemfile"]
 mtls = ["tls", "x509-parser"]
 tokio-macros = ["tokio/macros"]
@@ -74,7 +74,7 @@ tokio-stream = { version = "0.1.6", features = ["signal", "time"] }
 cookie = { version = "0.18", features = ["percent-encode"] }
 futures = { version = "0.3.30", default-features = false, features = ["std"] }
 state = "0.6"
-transient = { version = "0.3" }
+transient = { version = "0.4" }
 
 # tracing
 tracing = { version = "0.1.40", default-features = false, features = ["std", "attributes"] }
diff --git a/core/lib/src/form/error.rs b/core/lib/src/form/error.rs
index 002c2f28..5a01570b 100644
--- a/core/lib/src/form/error.rs
+++ b/core/lib/src/form/error.rs
@@ -8,7 +8,6 @@ use std::net::AddrParseError;
 use std::borrow::Cow;
 
 use serde::{Serialize, ser::{Serializer, SerializeStruct}};
-use transient::Transient;
 
 use crate::http::Status;
 use crate::form::name::{NameBuf, Name};
@@ -55,8 +54,9 @@ use crate::data::ByteUnit;
 ///     Ok(i)
 /// }
 /// ```
-#[derive(Default, Debug, PartialEq, Serialize, Transient)]
-#[variance('v = co)] // TODO: update when Transient v0.4
+#[derive(Default, Debug, PartialEq, Serialize)]
+// TODO: this is invariant wrt 'v, since Cow<'a, T> is invariant wrt T.
+// We need it to be covariant wrt 'v, so we can use it as an error type.
 #[serde(transparent)]
 pub struct Errors<'v>(Vec<Error<'v>>);
 
diff --git a/examples/error-handling/src/main.rs b/examples/error-handling/src/main.rs
index cdde474b..8f14eb42 100644
--- a/examples/error-handling/src/main.rs
+++ b/examples/error-handling/src/main.rs
@@ -5,31 +5,11 @@
 use rocket::{Rocket, Build};
 use rocket::response::{content, status};
 use rocket::http::{Status, uri::Origin};
-
-// Custom impl so I can implement Static (or Transient) ---
-// We should upstream implementations for most common error types
-// in transient itself
-use rocket::catcher::{Static};
 use std::num::ParseIntError;
 
-#[derive(Debug)]
-#[allow(unused)]
-struct IntErr(ParseIntError);
-impl Static for IntErr {}
-
-struct I8(i8);
-use rocket::request::FromParam;
-impl FromParam<'_> for I8 {
-    type Error = IntErr;
-    fn from_param(param: &str) -> Result<Self, Self::Error> {
-        param.parse::<i8>().map(Self).map_err(IntErr)
-    }
-}
-// ------------------------------
-
 #[get("/hello/<name>/<age>")]
-fn hello(name: &str, age: I8) -> String {
-    format!("Hello, {} year old named {}!", age.0, name)
+fn hello(name: &str, age: i8) -> String {
+    format!("Hello, {} year old named {}!", age, name)
 }
 
 #[get("/<code>")]
@@ -60,7 +40,7 @@ fn hello_not_found(uri: &Origin<'_>) -> content::RawHtml<String> {
 
 // `error` and `status` type. All other params must be `FromOrigin`?
 #[catch(422, error = "<e>" /*, status = "<_s>"*/)]
-fn param_error(e: &IntErr, uri: &Origin<'_>) -> content::RawHtml<String> {
+fn param_error(e: &ParseIntError, uri: &Origin<'_>) -> content::RawHtml<String> {
     content::RawHtml(format!("\
         <p>Sorry, but '{}' is not a valid path!</p>\
         <p>Try visiting /hello/&lt;name&gt;/&lt;age&gt; instead.</p>\
diff --git a/examples/error-handling/src/tests.rs b/examples/error-handling/src/tests.rs
index ad6e421a..a0f90dc1 100644
--- a/examples/error-handling/src/tests.rs
+++ b/examples/error-handling/src/tests.rs
@@ -1,6 +1,5 @@
 use rocket::local::blocking::Client;
 use rocket::http::Status;
-use super::{I8, IntErr};
 
 #[test]
 fn test_hello() {
@@ -11,7 +10,7 @@ fn test_hello() {
     let response = client.get(uri).dispatch();
 
     assert_eq!(response.status(), Status::Ok);
-    assert_eq!(response.into_string().unwrap(), super::hello(name, I8(age)));
+    assert_eq!(response.into_string().unwrap(), super::hello(name, age));
 }
 
 #[test]
@@ -50,7 +49,7 @@ fn test_hello_invalid_age() {
     for path in &["Ford/-129", "Trillian/128"] {
         let request = client.get(format!("/hello/{}", path));
         let expected = super::param_error(
-            &IntErr(path.split_once("/").unwrap().1.parse::<i8>().unwrap_err()),
+            &path.split_once("/").unwrap().1.parse::<i8>().unwrap_err(),
             request.uri()
         );
         let response = request.dispatch();