diff --git a/src/r0/contact/get_contacts.rs b/src/r0/contact/get_contacts.rs
index a67b2994..f033ce10 100644
--- a/src/r0/contact/get_contacts.rs
+++ b/src/r0/contact/get_contacts.rs
@@ -1,9 +1,12 @@
-//! [GET /_matrix/client/r0/account/3pid](https://matrix.org/docs/spec/client_server/r0.4.0.html#get-matrix-client-r0-account-3pid)
+//! [GET /_matrix/client/r0/account/3pid](https://matrix.org/docs/spec/client_server/r0.6.0#get-matrix-client-r0-account-3pid)
+
+use std::time::SystemTime;
 
-use crate::r0::thirdparty::Medium;
 use ruma_api::ruma_api;
 use serde::{Deserialize, Serialize};
 
+use crate::r0::thirdparty::Medium;
+
 ruma_api! {
     metadata {
         description: "Get a list of 3rd party contacts associated with the user's account.",
@@ -19,6 +22,7 @@ ruma_api! {
     response {
         /// A list of third party identifiers the homeserver has associated with the user's
         /// account.
+        #[serde(default, skip_serializing_if = "Vec::is_empty")]
         pub threepids: Vec<ThirdPartyIdentifier>,
     }
 
@@ -27,9 +31,51 @@ ruma_api! {
 
 /// An identifier external to Matrix.
 #[derive(Clone, Debug, Deserialize, Serialize)]
+#[cfg_attr(test, derive(PartialEq))]
 pub struct ThirdPartyIdentifier {
     /// The third party identifier address.
     pub address: String,
     /// The medium of third party identifier.
     pub medium: Medium,
+    /// The time when the identifier was validated by the identity server.
+    #[serde(with = "crate::serde::time::ms_since_unix_epoch")]
+    pub validated_at: SystemTime,
+    /// The time when the homeserver associated the third party identifier with the user.
+    #[serde(with = "crate::serde::time::ms_since_unix_epoch")]
+    pub added_at: SystemTime,
+}
+
+#[cfg(test)]
+mod tests {
+    use std::time::{Duration, UNIX_EPOCH};
+
+    use serde_json::{from_value as from_json_value, json, to_value as to_json_value};
+
+    use super::{Medium, ThirdPartyIdentifier};
+
+    #[test]
+    fn third_party_identifier_serde() {
+        let third_party_id = ThirdPartyIdentifier {
+            address: "monkey@banana.island".into(),
+            medium: Medium::Email,
+            validated_at: UNIX_EPOCH + Duration::from_millis(1535176800000),
+            added_at: UNIX_EPOCH + Duration::from_millis(1535336848756),
+        };
+
+        let third_party_id_serialized = json!({
+            "medium": "email",
+            "address": "monkey@banana.island",
+            "validated_at": 1535176800000u64,
+            "added_at": 1535336848756u64
+        });
+
+        assert_eq!(
+            to_json_value(third_party_id.clone()).unwrap(),
+            third_party_id_serialized.clone()
+        );
+        assert_eq!(
+            third_party_id,
+            from_json_value(third_party_id_serialized).unwrap()
+        );
+    }
 }
diff --git a/src/serde.rs b/src/serde.rs
index e89573d3..79c08e92 100644
--- a/src/serde.rs
+++ b/src/serde.rs
@@ -2,6 +2,7 @@
 
 pub mod duration;
 pub mod json_string;
+pub mod time;
 
 pub fn is_default<T: Default + PartialEq>(val: &T) -> bool {
     val == &T::default()
diff --git a/src/serde/time.rs b/src/serde/time.rs
new file mode 100644
index 00000000..8605814c
--- /dev/null
+++ b/src/serde/time.rs
@@ -0,0 +1,3 @@
+//! De-/serialization functions for `std::time::SystemTime` objects
+
+pub mod ms_since_unix_epoch;
diff --git a/src/serde/time/ms_since_unix_epoch.rs b/src/serde/time/ms_since_unix_epoch.rs
new file mode 100644
index 00000000..ea1b79cc
--- /dev/null
+++ b/src/serde/time/ms_since_unix_epoch.rs
@@ -0,0 +1,78 @@
+//! De-/serialization functions for `std::time::SystemTime` objects represented as milliseconds
+//! since the UNIX epoch. Delegates to `js_int::UInt` to ensure integer size is within bounds.
+
+use std::{
+    convert::TryFrom,
+    time::{Duration, SystemTime, UNIX_EPOCH},
+};
+
+use js_int::UInt;
+use serde::{
+    de::{Deserialize, Deserializer},
+    ser::{Error, Serialize, Serializer},
+};
+
+/// Serialize a SystemTime.
+///
+/// Will fail if integer is greater than the maximum integer that can be unambiguously represented
+/// by an f64.
+pub fn serialize<S>(time: &SystemTime, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+{
+    // If this unwrap fails, the system this is executed is completely broken.
+    let time_since_epoch = time.duration_since(UNIX_EPOCH).unwrap();
+    match UInt::try_from(time_since_epoch.as_millis()) {
+        Ok(uint) => uint.serialize(serializer),
+        Err(err) => Err(S::Error::custom(err)),
+    }
+}
+
+/// Deserializes a SystemTime.
+///
+/// Will fail if integer is greater than the maximum integer that can be unambiguously represented
+/// by an f64.
+pub fn deserialize<'de, D>(deserializer: D) -> Result<SystemTime, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let millis = UInt::deserialize(deserializer)?;
+    Ok(UNIX_EPOCH + Duration::from_millis(millis.into()))
+}
+
+#[cfg(test)]
+mod tests {
+    use std::time::{Duration, SystemTime, UNIX_EPOCH};
+
+    use serde::{Deserialize, Serialize};
+    use serde_json::json;
+
+    #[derive(Clone, Debug, PartialEq, Deserialize, Serialize)]
+    struct SystemTimeTest {
+        #[serde(with = "super")]
+        timestamp: SystemTime,
+    }
+
+    #[test]
+    fn test_deserialize() {
+        let json = json!({ "timestamp": 3000 });
+
+        assert_eq!(
+            serde_json::from_value::<SystemTimeTest>(json).unwrap(),
+            SystemTimeTest {
+                timestamp: UNIX_EPOCH + Duration::from_millis(3000),
+            },
+        );
+    }
+
+    #[test]
+    fn test_serialize() {
+        let request = SystemTimeTest {
+            timestamp: UNIX_EPOCH + Duration::new(2, 0),
+        };
+        assert_eq!(
+            serde_json::to_value(&request).unwrap(),
+            json!({ "timestamp": 2000 })
+        );
+    }
+}