diff --git a/Cargo.toml b/Cargo.toml
index 836b552..a9c62b2 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -22,6 +22,7 @@ reqwest = { version = "0.11.4", features = ["json"], optional = true }
 tokio = { version = "1.9.0", features = ["sync"], optional = true }
 openssl-sys = "0.9.65"
 foreign-types = "0.3.2"
+serde_with = "3.1.0"
 
 [dev-dependencies]
 axum = "0.1.3"
diff --git a/src/lib.rs b/src/lib.rs
index 0db2e2b..5568c4f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,15 +1,4 @@
 #![doc = include_str!("../README.md")]
-mod some;
-
-pub mod hmac;
-
-pub mod eddsa;
-
-pub mod ecdsa;
-
-pub mod rsa;
-
-pub mod jwk;
 
 use std::{
     borrow::Cow,
@@ -18,13 +7,27 @@ use std::{
     string::FromUtf8Error,
     time::{Duration, SystemTime, UNIX_EPOCH},
 };
-
-use jwk::Jwk;
 use openssl::error::ErrorStack;
 use serde::{de::DeserializeOwned, Deserialize, Serialize};
 use serde_json::{Map, Value};
+use serde_with::serde_as;
 use smallvec::SmallVec;
 
+use jwk::Jwk;
+pub use some::*;
+
+mod some;
+
+pub mod hmac;
+
+pub mod eddsa;
+
+pub mod ecdsa;
+
+pub mod rsa;
+
+pub mod jwk;
+
 /// JWT header.
 #[non_exhaustive]
 #[derive(Debug, Serialize, Deserialize, Default)]
@@ -65,15 +68,16 @@ impl<T> Default for OneOrMany<T> {
 }
 
 /// JWT Claims.
+#[serde_as]
 #[non_exhaustive]
 #[derive(Debug, Serialize, Default, Deserialize)]
 pub struct Claims<ExtraClaims> {
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub exp: Option<u64>,
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub nbf: Option<u64>,
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub iat: Option<u64>,
+    #[serde_as(as = "Option<serde_with::DurationSeconds<f64>>")]
+    pub exp: Option<Duration>,
+    #[serde_as(as = "Option<serde_with::DurationSeconds<f64>>")]
+    pub nbf: Option<Duration>,
+    #[serde_as(as = "Option<serde_with::DurationSeconds<f64>>")]
+    pub iat: Option<Duration>,
 
     #[serde(skip_serializing_if = "Option::is_none")]
     pub iss: Option<String>,
@@ -189,8 +193,7 @@ impl<ExtraClaims> HeaderAndClaims<ExtraClaims> {
         self.claims.iat = Some(
             SystemTime::now()
                 .duration_since(SystemTime::UNIX_EPOCH)
-                .unwrap()
-                .as_secs(),
+                .unwrap(),
         );
         self
     }
@@ -198,7 +201,7 @@ impl<ExtraClaims> HeaderAndClaims<ExtraClaims> {
     /// Check that `iat` is present and is later than `t`.
     pub fn iat_is_later_than(&self, t: SystemTime) -> bool {
         self.claims.iat.map_or(false, |iat| {
-            iat > t.duration_since(UNIX_EPOCH).unwrap().as_secs()
+            iat > t.duration_since(UNIX_EPOCH).unwrap()
         })
     }
 
@@ -209,7 +212,7 @@ impl<ExtraClaims> HeaderAndClaims<ExtraClaims> {
             .duration_since(SystemTime::UNIX_EPOCH)
             .unwrap()
             .as_secs();
-        self.claims.exp = Some(t);
+        self.claims.exp = Some(Duration::from_secs(t));
         self
     }
 
@@ -220,7 +223,7 @@ impl<ExtraClaims> HeaderAndClaims<ExtraClaims> {
             .duration_since(SystemTime::UNIX_EPOCH)
             .unwrap()
             .as_secs();
-        self.claims.nbf = Some(t);
+        self.claims.nbf = Some(Duration::from_secs(t));
         self
     }
 }
@@ -238,8 +241,6 @@ fn url_safe_trailing_bits() -> base64::Config {
     base64::URL_SAFE_NO_PAD.decode_allow_trailing_bits(true)
 }
 
-pub use some::*;
-
 /// Encode and sign this header and claims with the signing key.
 ///
 /// The `alg` field in header is automatically set. The `kid` claim is
@@ -286,13 +287,13 @@ pub fn verify<ExtraClaims: DeserializeOwned>(
     // Check exp and nbf.
     let now = SystemTime::now();
     if let Some(exp) = claims.claims.exp {
-        let exp = SystemTime::UNIX_EPOCH + Duration::from_secs(exp);
+        let exp = SystemTime::UNIX_EPOCH + exp;
         if now > exp {
             return Err(Error::Expired);
         }
     }
     if let Some(nbf) = claims.claims.nbf {
-        let nbf = SystemTime::UNIX_EPOCH + Duration::from_secs(nbf);
+        let nbf = SystemTime::UNIX_EPOCH + nbf;
         if now < nbf {
             return Err(Error::Before);
         }
@@ -496,6 +497,8 @@ pub type Result<T> = std::result::Result<T, Error>;
 
 #[cfg(test)]
 mod tests {
+    use base64::{CharacterSet, Config};
+
     use crate::ecdsa::{EcdsaAlgorithm, EcdsaPrivateKey};
 
     use super::*;
@@ -532,4 +535,15 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn claim_deserialization() {
+        let mut json = r#"eyJpYXQiOjEuNjkyMTkwMTI1RTksImV4cCI6MS42OTIxOTM3MjVFOSwiYW50aUNzcmZUb2tlbiI6bnVsbCwic3ViIjoiYTM5ZmZjNWUtNjc5ZC00YjAzLWI5YmYtYTliZjEzNDk4NGYzIiwiaXNzIjoiaHR0cDovL2xvY2FsaG9zdDozOTk5L2F1dGgiLCJzZXNzaW9uSGFuZGxlIjoiNTAyMWQ2MTQtYzFmNi00ZTZkLWI1NjktZGQxN2Q0N2EyOWI0IiwicGFyZW50UmVmcmVzaFRva2VuSGFzaDEiOm51bGwsInJlZnJlc2hUb2tlbkhhc2gxIjoiNTZiMjcxZDcxNGRlMzg3M2UwMmIyZjAyYTJiZDcyYWJjZDIyZDM0NGZlZjE2YTJkMWJjYmM1NGU2YWUxN2M3OCJ9"#.as_bytes();
+
+        let r = base64::read::DecoderReader::new(&mut json, Config::new(CharacterSet::ImapMutf7, true));
+
+        let claims: Claims<Value> = serde_json::from_reader(r).unwrap();
+        assert_eq!(claims.iat, Some(Duration::from_secs(1692190125)));
+        assert_eq!(claims.exp, Some(Duration::from_secs(1692193725)));
+    }
 }