diff --git a/Cargo.toml b/Cargo.toml
index b7830a7d..ab35f757 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -101,7 +101,7 @@ serde = { version = "1.0", default-features = false, features = ["derive", "rc"]
 serde_bytes = "0.11"
 serde_json = "1.0"
 toml = { version = "0.8", default-features = false, features = ["parse"] }
-utoipa = "5.3.1"
+utoipa = { version = "5.3.1", features = ["chrono"] }
 
 # newer version requires rust edition 2021
 k8s-openapi = { version = "0.21", features = ["v1_24"] }
diff --git a/doc/api/garage-admin-v2.json b/doc/api/garage-admin-v2.json
index 6ede967b..8f3517cb 100644
--- a/doc/api/garage-admin-v2.json
+++ b/doc/api/garage-admin-v2.json
@@ -2053,6 +2053,7 @@
               "string",
               "null"
             ],
+            "format": "date-time",
             "description": "Expiration time and date, formatted according to RFC 3339"
           },
           "expired": {
@@ -3639,6 +3640,7 @@
               "string",
               "null"
             ],
+            "format": "date-time",
             "description": "Expiration time and date, formatted according to RFC 3339"
           },
           "name": {
diff --git a/src/api/admin/api.rs b/src/api/admin/api.rs
index 94cb7377..11ffb772 100644
--- a/src/api/admin/api.rs
+++ b/src/api/admin/api.rs
@@ -317,7 +317,6 @@ pub struct GetAdminTokenInfoResponse {
 	/// Name of the admin API token
 	pub name: String,
 	/// Expiration time and date, formatted according to RFC 3339
-	#[schema(value_type = Option<String>)]
 	pub expiration: Option<chrono::DateTime<chrono::Utc>>,
 	/// Whether this admin token is expired already
 	pub expired: bool,
@@ -357,7 +356,6 @@ pub struct UpdateAdminTokenRequestBody {
 	/// Name of the admin API token
 	pub name: Option<String>,
 	/// Expiration time and date, formatted according to RFC 3339
-	#[schema(value_type = Option<String>)]
 	pub expiration: Option<chrono::DateTime<chrono::Utc>>,
 	/// Scope of the admin API token, a list of admin endpoint names (such as
 	/// `GetClusterStatus`, etc), or the special value `*` to allow all