diff --git a/Cargo.toml b/Cargo.toml
index 34e31ccc..0ded5316 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,8 +14,9 @@ edition = "2018"
 
 [dependencies]
 js_int = { version = "0.1.4", features = ["serde"] }
-ruma-identifiers = "0.15.1"
 ruma-events-macros = { path = "ruma-events-macros", version = "=0.3.0" }
+ruma-identifiers = "0.15.1"
+ruma-serde = "0.1.0"
 serde = { version = "1.0.106", features = ["derive"] }
 serde_json = "1.0.51"
 
diff --git a/ruma-events-macros/src/gen.rs b/ruma-events-macros/src/gen.rs
index 9a5c587f..8dc09837 100644
--- a/ruma-events-macros/src/gen.rs
+++ b/ruma-events-macros/src/gen.rs
@@ -134,9 +134,8 @@ impl ToTokens for RumaEvent {
                             &self.event_id
                         }
 
-                        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this event was
-                        /// sent.
-                        fn origin_server_ts(&self) -> js_int::UInt {
+                        /// Time on originating homeserver when this event was sent.
+                        fn origin_server_ts(&self) -> std::time::SystemTime {
                             self.origin_server_ts
                         }
 
@@ -284,9 +283,9 @@ fn populate_room_event_fields(content_name: Ident, fields: Vec<Field>) -> Vec<Fi
         /// The unique identifier for the event.
         pub event_id: ruma_identifiers::EventId,
 
-        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-        /// event was sent.
-        pub origin_server_ts: js_int::UInt,
+        /// Time on originating homeserver when this event was sent.
+        #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+        pub origin_server_ts: std::time::SystemTime,
 
         /// The unique identifier for the room associated with this event.
         #[serde(skip_serializing_if = "Option::is_none")]
diff --git a/src/key/verification/request.rs b/src/key/verification/request.rs
index 77e9dcfb..34bc7814 100644
--- a/src/key/verification/request.rs
+++ b/src/key/verification/request.rs
@@ -1,6 +1,7 @@
 //! Types for the *m.key.verification.request* event.
 
-use js_int::UInt;
+use std::time::SystemTime;
+
 use ruma_events_macros::ruma_event;
 use ruma_identifiers::DeviceId;
 
@@ -25,11 +26,12 @@ ruma_event! {
             /// The verification methods supported by the sender.
             pub methods: Vec<VerificationMethod>,
 
-            /// The POSIX timestamp in milliseconds for when the request was made.
+            /// The time in milliseconds for when the request was made.
             ///
             /// If the request is in the future by more than 5 minutes or more than 10 minutes in
             /// the past, the message should be ignored by the receiver.
-            pub timestamp: UInt,
+            #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+            pub timestamp: SystemTime,
         },
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index 0c82f4e1..756f5577 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -118,9 +118,9 @@
 use std::{
     error::Error,
     fmt::{Debug, Display, Formatter, Result as FmtResult},
+    time::SystemTime,
 };
 
-use js_int::UInt;
 use ruma_identifiers::{EventId, RoomId, UserId};
 use serde::{
     de::{MapAccess, Visitor},
@@ -381,9 +381,8 @@ pub trait RoomEvent: Event {
     /// The unique identifier for the event.
     fn event_id(&self) -> &EventId;
 
-    /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this event was
-    /// sent.
-    fn origin_server_ts(&self) -> UInt;
+    /// Time on originating homeserver when this event was sent.
+    fn origin_server_ts(&self) -> SystemTime;
 
     /// The unique identifier for the room associated with this event.
     ///
@@ -458,6 +457,8 @@ mod custom {
 }
 
 mod custom_room {
+    use std::time::SystemTime;
+
     use super::{Event, EventType, RoomEvent};
 
     use ruma_events_macros::FromRaw;
@@ -474,9 +475,9 @@ mod custom_room {
         /// The custom type of the event.
         #[serde(rename = "type")]
         pub event_type: String,
-        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-        /// event was sent.
-        pub origin_server_ts: js_int::UInt,
+        /// Time on originating homeserver when this event was sent.
+        #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+        pub origin_server_ts: SystemTime,
         /// The unique identifier for the room associated with this event.
         pub room_id: Option<ruma_identifiers::RoomId>,
         /// The unique identifier for the user who sent this event.
@@ -507,9 +508,8 @@ mod custom_room {
         fn event_id(&self) -> &ruma_identifiers::EventId {
             &self.event_id
         }
-        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this event was
-        /// sent.
-        fn origin_server_ts(&self) -> js_int::UInt {
+        /// Time on originating homeserver when this event was sent.
+        fn origin_server_ts(&self) -> SystemTime {
             self.origin_server_ts
         }
         /// The unique identifier for the room associated with this event.
@@ -542,9 +542,9 @@ mod custom_room {
             /// The custom type of the event.
             #[serde(rename = "type")]
             pub event_type: String,
-            /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-            /// event was sent.
-            pub origin_server_ts: js_int::UInt,
+            /// Time on originating homeserver when this event was sent.
+            #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+            pub origin_server_ts: SystemTime,
             /// The unique identifier for the room associated with this event.
             pub room_id: Option<ruma_identifiers::RoomId>,
             /// The unique identifier for the user who sent this event.
@@ -557,6 +557,8 @@ mod custom_room {
 }
 
 mod custom_state {
+    use std::time::SystemTime;
+
     use super::{Event, EventType, RoomEvent, StateEvent};
 
     use ruma_events_macros::FromRaw;
@@ -573,9 +575,9 @@ mod custom_state {
         /// The custom type of the event.
         #[serde(rename = "type")]
         pub event_type: String,
-        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-        /// event was sent.
-        pub origin_server_ts: js_int::UInt,
+        /// Time on originating homeserver when this event was sent.
+        #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+        pub origin_server_ts: SystemTime,
         /// The previous content for this state key, if any.
         pub prev_content: Option<CustomStateEventContent>,
         /// The unique identifier for the room associated with this event.
@@ -610,9 +612,8 @@ mod custom_state {
         fn event_id(&self) -> &ruma_identifiers::EventId {
             &self.event_id
         }
-        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this event was
-        /// sent.
-        fn origin_server_ts(&self) -> js_int::UInt {
+        /// Time on originating homeserver when this event was sent.
+        fn origin_server_ts(&self) -> SystemTime {
             self.origin_server_ts
         }
         /// The unique identifier for the room associated with this event.
@@ -656,9 +657,9 @@ mod custom_state {
             /// The custom type of the event.
             #[serde(rename = "type")]
             pub event_type: String,
-            /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-            /// event was sent.
-            pub origin_server_ts: js_int::UInt,
+            /// Time on originating homeserver when this event was sent.
+            #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+            pub origin_server_ts: SystemTime,
             /// The previous content for this state key, if any.
             pub prev_content: Option<CustomStateEventContent>,
             /// The unique identifier for the room associated with this event.
diff --git a/src/macros.rs b/src/macros.rs
index b2bb7bbb..fede51ea 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -53,9 +53,8 @@ macro_rules! impl_room_event {
                 &self.event_id
             }
 
-            /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this event was
-            /// sent.
-            fn origin_server_ts(&self) -> UInt {
+            /// Time on originating homeserver when this event was sent.
+            fn origin_server_ts(&self) -> ::std::time::SystemTime {
                 self.origin_server_ts
             }
 
@@ -63,17 +62,17 @@ macro_rules! impl_room_event {
             ///
             /// This can be `None` if the event came from a context where there is
             /// no ambiguity which room it belongs to, like a `/sync` response for example.
-            fn room_id(&self) -> Option<&RoomId> {
+            fn room_id(&self) -> Option<&::ruma_identifiers::RoomId> {
                 self.room_id.as_ref()
             }
 
             /// The unique identifier for the user who sent this event.
-            fn sender(&self) -> &UserId {
+            fn sender(&self) -> &::ruma_identifiers::UserId {
                 &self.sender
             }
 
             /// Additional key-value pairs not signed by the homeserver.
-            fn unsigned(&self) -> &serde_json::Map<String, serde_json::Value> {
+            fn unsigned(&self) -> &::serde_json::Map<String, ::serde_json::Value> {
                 &self.unsigned
             }
         }
@@ -100,7 +99,7 @@ macro_rules! impl_state_event {
 
 macro_rules! impl_from_for_enum {
     ($self_ty:ident, $inner_ty:ty, $variant:ident) => {
-        impl From<$inner_ty> for $self_ty {
+        impl ::std::convert::From<$inner_ty> for $self_ty {
             fn from(event: $inner_ty) -> Self {
                 $self_ty::$variant(event)
             }
diff --git a/src/receipt.rs b/src/receipt.rs
index afd69c5e..8c63ed22 100644
--- a/src/receipt.rs
+++ b/src/receipt.rs
@@ -1,8 +1,7 @@
 //! Types for the *m.receipt* event.
 
-use std::collections::HashMap;
+use std::{collections::HashMap, time::SystemTime};
 
-use js_int::UInt;
 use ruma_events_macros::ruma_event;
 use ruma_identifiers::{EventId, RoomId, UserId};
 use serde::{Deserialize, Serialize};
@@ -44,8 +43,13 @@ pub struct Receipts {
 pub type UserReceipts = HashMap<UserId, Receipt>;
 
 /// An acknowledgement of an event.
-#[derive(Clone, Debug, Deserialize, PartialEq, Serialize)]
+#[derive(Clone, Debug, PartialEq, Deserialize, Serialize)]
 pub struct Receipt {
-    /// The timestamp (milliseconds since the Unix epoch) when the receipt was sent.
-    pub ts: Option<UInt>,
+    /// The time when the receipt was sent.
+    #[serde(
+        with = "ruma_serde::time::opt_ms_since_unix_epoch",
+        default,
+        skip_serializing_if = "Option::is_none"
+    )]
+    pub ts: Option<SystemTime>,
 }
diff --git a/src/room/canonical_alias.rs b/src/room/canonical_alias.rs
index fde83469..1753580e 100644
--- a/src/room/canonical_alias.rs
+++ b/src/room/canonical_alias.rs
@@ -1,8 +1,15 @@
 //! Types for the *m.room.canonical_alias* event.
 
-use js_int::UInt;
+use std::{
+    convert::TryFrom,
+    time::{SystemTime, UNIX_EPOCH},
+};
+
 use ruma_identifiers::{EventId, RoomAliasId, RoomId, UserId};
-use serde::{ser::SerializeStruct, Deserialize, Serialize, Serializer};
+use serde::{
+    ser::{Error, SerializeStruct},
+    Deserialize, Serialize, Serializer,
+};
 use serde_json::{Map, Value};
 
 use crate::{util::empty_string_as_none, Event, EventType, FromRaw};
@@ -16,9 +23,8 @@ pub struct CanonicalAliasEvent {
     /// The unique identifier for the event.
     pub event_id: EventId,
 
-    /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-    /// event was sent.
-    pub origin_server_ts: UInt,
+    /// Time on originating homeserver when this event was sent.
+    pub origin_server_ts: SystemTime,
 
     /// The previous content for this state key, if any.
     pub prev_content: Option<CanonicalAliasEventContent>,
@@ -93,7 +99,15 @@ impl Serialize for CanonicalAliasEvent {
 
         state.serialize_field("content", &self.content)?;
         state.serialize_field("event_id", &self.event_id)?;
-        state.serialize_field("origin_server_ts", &self.origin_server_ts)?;
+
+        let origin_server_ts = js_int::UInt::try_from(
+            self.origin_server_ts
+                .duration_since(UNIX_EPOCH)
+                .unwrap()
+                .as_millis(),
+        )
+        .map_err(S::Error::custom)?;
+        state.serialize_field("origin_server_ts", &origin_server_ts)?;
 
         if self.prev_content.is_some() {
             state.serialize_field("prev_content", &self.prev_content)?;
@@ -133,9 +147,9 @@ pub(crate) mod raw {
         /// The unique identifier for the event.
         pub event_id: EventId,
 
-        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-        /// event was sent.
-        pub origin_server_ts: UInt,
+        /// Time on originating homeserver when this event was sent.
+        #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+        pub origin_server_ts: SystemTime,
 
         /// The previous content for this state key, if any.
         pub prev_content: Option<CanonicalAliasEventContent>,
@@ -170,9 +184,11 @@ pub(crate) mod raw {
 
 #[cfg(test)]
 mod tests {
-    use std::convert::TryFrom;
+    use std::{
+        convert::TryFrom,
+        time::{Duration, UNIX_EPOCH},
+    };
 
-    use js_int::UInt;
     use ruma_identifiers::{EventId, RoomAliasId, UserId};
     use serde_json::{from_value as from_json_value, json, to_value as to_json_value, Map};
 
@@ -186,7 +202,7 @@ mod tests {
                 alias: Some(RoomAliasId::try_from("#somewhere:localhost").unwrap()),
             },
             event_id: EventId::try_from("$h29iv0s8:example.com").unwrap(),
-            origin_server_ts: UInt::try_from(1).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1),
             prev_content: None,
             room_id: None,
             sender: UserId::try_from("@carl:example.com").unwrap(),
diff --git a/src/room/encrypted.rs b/src/room/encrypted.rs
index 417b70b3..5ebf4626 100644
--- a/src/room/encrypted.rs
+++ b/src/room/encrypted.rs
@@ -1,5 +1,6 @@
 //! Types for the *m.room.encrypted* event.
-use std::collections::HashMap;
+
+use std::{collections::HashMap, time::SystemTime};
 
 use js_int::UInt;
 use ruma_identifiers::{DeviceId, EventId, RoomId, UserId};
@@ -21,9 +22,9 @@ pub struct EncryptedEvent {
     /// The unique identifier for the event.
     pub event_id: EventId,
 
-    /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-    /// event was sent.
-    pub origin_server_ts: UInt,
+    /// Time on originating homeserver when this event was sent.
+    #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+    pub origin_server_ts: SystemTime,
 
     /// The unique identifier for the room associated with this event.
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -121,9 +122,9 @@ pub(crate) mod raw {
         /// The unique identifier for the event.
         pub event_id: EventId,
 
-        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-        /// event was sent.
-        pub origin_server_ts: UInt,
+        /// Time on originating homeserver when this event was sent.
+        #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+        pub origin_server_ts: SystemTime,
 
         /// The unique identifier for the room associated with this event.
         pub room_id: Option<RoomId>,
diff --git a/src/room/member.rs b/src/room/member.rs
index c497956b..81433c1c 100644
--- a/src/room/member.rs
+++ b/src/room/member.rs
@@ -221,9 +221,11 @@ impl MemberEvent {
 
 #[cfg(test)]
 mod tests {
-    use std::convert::TryFrom;
+    use std::{
+        convert::TryFrom,
+        time::{Duration, UNIX_EPOCH},
+    };
 
-    use js_int::UInt;
     use ruma_identifiers::{EventId, RoomId, UserId};
     use serde_json::{json, Map};
 
@@ -241,7 +243,7 @@ mod tests {
                 third_party_invite: None,
             },
             event_id: EventId::try_from("$h29iv0s8:example.com").unwrap(),
-            origin_server_ts: UInt::new(1).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1),
             room_id: Some(RoomId::try_from("!n8f893n9:example.com").unwrap()),
             sender: UserId::try_from("@carl:example.com").unwrap(),
             state_key: "example.com".to_string(),
@@ -273,7 +275,7 @@ mod tests {
                 third_party_invite: None,
             },
             event_id: EventId::try_from("$h29iv0s8:example.com").unwrap(),
-            origin_server_ts: UInt::new(1).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1),
             room_id: Some(RoomId::try_from("!n8f893n9:example.com").unwrap()),
             sender: UserId::try_from("@carl:example.com").unwrap(),
             state_key: "example.com".to_string(),
@@ -329,7 +331,7 @@ mod tests {
                 }),
             },
             event_id: EventId::try_from("$143273582443PhrSn:example.org").unwrap(),
-            origin_server_ts: UInt::new(233).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(233),
             room_id: Some(RoomId::try_from("!jEsUZKDJdhlrceRyVU:example.org").unwrap()),
             sender: UserId::try_from("@alice:example.org").unwrap(),
             state_key: "@alice:example.org".to_string(),
@@ -384,7 +386,7 @@ mod tests {
                 third_party_invite: None,
             },
             event_id: EventId::try_from("$143273582443PhrSn:example.org").unwrap(),
-            origin_server_ts: UInt::new(233).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(233),
             room_id: Some(RoomId::try_from("!jEsUZKDJdhlrceRyVU:example.org").unwrap()),
             sender: UserId::try_from("@alice:example.org").unwrap(),
             state_key: "@alice:example.org".to_string(),
diff --git a/src/room/message.rs b/src/room/message.rs
index 9f190157..820723e9 100644
--- a/src/room/message.rs
+++ b/src/room/message.rs
@@ -1,5 +1,7 @@
 //! Types for the *m.room.message* event.
 
+use std::time::SystemTime;
+
 use js_int::UInt;
 use ruma_identifiers::{EventId, RoomId, UserId};
 use serde::{ser::SerializeStruct, Deserialize, Deserializer, Serialize, Serializer};
@@ -20,9 +22,9 @@ pub struct MessageEvent {
     /// The unique identifier for the event.
     pub event_id: EventId,
 
-    /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-    /// event was sent.
-    pub origin_server_ts: UInt,
+    /// Time on originating homeserver when this event was sent.
+    #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+    pub origin_server_ts: SystemTime,
 
     /// The unique identifier for the room associated with this event.
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -149,9 +151,9 @@ pub(crate) mod raw {
         /// The unique identifier for the event.
         pub event_id: EventId,
 
-        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-        /// event was sent.
-        pub origin_server_ts: UInt,
+        /// Time on originating homeserver when this event was sent.
+        #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+        pub origin_server_ts: SystemTime,
 
         /// The unique identifier for the room associated with this event.
         pub room_id: Option<RoomId>,
diff --git a/src/room/name.rs b/src/room/name.rs
index c166baca..857acfb2 100644
--- a/src/room/name.rs
+++ b/src/room/name.rs
@@ -1,6 +1,7 @@
 //! Types for the *m.room.name* event.
 
-use js_int::UInt;
+use std::time::SystemTime;
+
 use ruma_identifiers::{EventId, RoomId, UserId};
 use serde::{Deserialize, Serialize};
 use serde_json::{Map, Value};
@@ -17,9 +18,9 @@ pub struct NameEvent {
     /// The unique identifier for the event.
     pub event_id: EventId,
 
-    /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-    /// event was sent.
-    pub origin_server_ts: UInt,
+    /// Time on originating homeserver when this event was sent.
+    #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+    pub origin_server_ts: SystemTime,
 
     /// The previous content for this state key, if any.
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -117,9 +118,9 @@ pub(crate) mod raw {
         /// The unique identifier for the event.
         pub event_id: EventId,
 
-        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-        /// event was sent.
-        pub origin_server_ts: UInt,
+        /// Time on originating homeserver when this event was sent.
+        #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+        pub origin_server_ts: SystemTime,
 
         /// The previous content for this state key, if any.
         pub prev_content: Option<NameEventContent>,
@@ -152,9 +153,12 @@ pub(crate) mod raw {
 
 #[cfg(test)]
 mod tests {
-    use std::{convert::TryFrom, iter::FromIterator};
+    use std::{
+        convert::TryFrom,
+        iter::FromIterator,
+        time::{Duration, UNIX_EPOCH},
+    };
 
-    use js_int::UInt;
     use ruma_identifiers::{EventId, RoomId, UserId};
     use serde_json::{from_value as from_json_value, json, to_value as to_json_value, Map};
 
@@ -169,7 +173,7 @@ mod tests {
                 name: Some("The room name".to_string()),
             },
             event_id: EventId::try_from("$h29iv0s8:example.com").unwrap(),
-            origin_server_ts: UInt::try_from(1).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1),
             prev_content: None,
             room_id: None,
             sender: UserId::try_from("@carl:example.com").unwrap(),
@@ -199,7 +203,7 @@ mod tests {
                 name: Some("The room name".to_string()),
             },
             event_id: EventId::try_from("$h29iv0s8:example.com").unwrap(),
-            origin_server_ts: UInt::try_from(1).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1),
             prev_content: Some(NameEventContent {
                 name: Some("The old name".to_string()),
             }),
diff --git a/src/room/pinned_events.rs b/src/room/pinned_events.rs
index 8bb84d5e..631706f3 100644
--- a/src/room/pinned_events.rs
+++ b/src/room/pinned_events.rs
@@ -17,9 +17,8 @@ ruma_event! {
 
 #[cfg(test)]
 mod tests {
-    use std::convert::TryFrom;
+    use std::time::{Duration, UNIX_EPOCH};
 
-    use js_int::UInt;
     use ruma_identifiers::{EventId, RoomId, UserId};
     use serde_json::{to_string, Map};
 
@@ -38,7 +37,7 @@ mod tests {
         let event = PinnedEventsEvent {
             content: content.clone(),
             event_id: EventId::new("example.com").unwrap(),
-            origin_server_ts: UInt::try_from(1_432_804_485_886u64).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1_432_804_485_886u64),
             prev_content: None,
             room_id: Some(RoomId::new("example.com").unwrap()),
             sender: UserId::new("example.com").unwrap(),
diff --git a/src/room/power_levels.rs b/src/room/power_levels.rs
index 127b6e8e..4b8a0705 100644
--- a/src/room/power_levels.rs
+++ b/src/room/power_levels.rs
@@ -1,8 +1,8 @@
 //! Types for the *m.room.power_levels* event.
 
-use std::collections::HashMap;
+use std::{collections::HashMap, time::SystemTime};
 
-use js_int::{Int, UInt};
+use js_int::Int;
 use ruma_identifiers::{EventId, RoomId, UserId};
 use serde::{Deserialize, Serialize};
 use serde_json::{Map, Value};
@@ -19,9 +19,9 @@ pub struct PowerLevelsEvent {
     /// The unique identifier for the event.
     pub event_id: EventId,
 
-    /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-    /// event was sent.
-    pub origin_server_ts: UInt,
+    /// Time on originating homeserver when this event was sent.
+    #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+    pub origin_server_ts: SystemTime,
 
     /// The previous content for this state key, if any.
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -146,9 +146,9 @@ pub(crate) mod raw {
         /// The unique identifier for the event.
         pub event_id: EventId,
 
-        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-        /// event was sent.
-        pub origin_server_ts: UInt,
+        /// Time on originating homeserver when this event was sent.
+        #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+        pub origin_server_ts: SystemTime,
 
         /// The previous content for this state key, if any.
         pub prev_content: Option<PowerLevelsEventContent>,
@@ -262,9 +262,13 @@ fn is_power_level_zero(l: &Int) -> bool {
 
 #[cfg(test)]
 mod tests {
-    use std::{collections::HashMap, convert::TryFrom};
+    use std::{
+        collections::HashMap,
+        convert::TryFrom,
+        time::{Duration, UNIX_EPOCH},
+    };
 
-    use js_int::{Int, UInt};
+    use js_int::Int;
     use maplit::hashmap;
     use ruma_identifiers::{EventId, RoomId, UserId};
     use serde_json::{json, to_value as to_json_value, Map};
@@ -292,7 +296,7 @@ mod tests {
                 notifications: NotificationPowerLevels::default(),
             },
             event_id: EventId::try_from("$h29iv0s8:example.com").unwrap(),
-            origin_server_ts: UInt::from(1u32),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1),
             prev_content: None,
             room_id: None,
             unsigned: Map::new(),
@@ -336,7 +340,7 @@ mod tests {
                 },
             },
             event_id: EventId::try_from("$h29iv0s8:example.com").unwrap(),
-            origin_server_ts: UInt::from(1u32),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1),
             prev_content: Some(PowerLevelsEventContent {
                 // Make just one field different so we at least know they're two different objects.
                 ban: Int::from(42),
diff --git a/src/room/server_acl.rs b/src/room/server_acl.rs
index d191c553..130ccc4b 100644
--- a/src/room/server_acl.rs
+++ b/src/room/server_acl.rs
@@ -1,6 +1,7 @@
 //! Types for the *m.room.server_acl* event.
 
-use js_int::UInt;
+use std::time::SystemTime;
+
 use ruma_identifiers::{EventId, RoomId, UserId};
 use serde::{Deserialize, Serialize};
 use serde_json::{Map, Value};
@@ -17,9 +18,9 @@ pub struct ServerAclEvent {
     /// The unique identifier for the event.
     pub event_id: EventId,
 
-    /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-    /// event was sent.
-    pub origin_server_ts: UInt,
+    /// Time on originating homeserver when this event was sent.
+    #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+    pub origin_server_ts: SystemTime,
 
     /// The previous content for this state key, if any.
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -116,9 +117,9 @@ pub(crate) mod raw {
         /// The unique identifier for the event.
         pub event_id: EventId,
 
-        /// Timestamp (milliseconds since the UNIX epoch) on originating homeserver when this
-        /// event was sent.
-        pub origin_server_ts: UInt,
+        /// Time on originating homeserver when this event was sent.
+        #[serde(with = "ruma_serde::time::ms_since_unix_epoch")]
+        pub origin_server_ts: SystemTime,
 
         /// The previous content for this state key, if any.
         pub prev_content: Option<ServerAclEventContent>,
diff --git a/src/to_device.rs b/src/to_device.rs
index ae464697..587c7e8a 100644
--- a/src/to_device.rs
+++ b/src/to_device.rs
@@ -256,9 +256,10 @@ mod raw {
 
 #[cfg(test)]
 mod tests {
-    use std::convert::TryFrom;
-
-    use js_int::UInt;
+    use std::{
+        convert::TryFrom,
+        time::{Duration, UNIX_EPOCH},
+    };
 
     use ruma_identifiers::{RoomId, UserId};
     use serde_json::{from_value as from_json_value, json};
@@ -647,7 +648,7 @@ mod tests {
         assert_eq!(event.content.methods, &[VerificationMethod::MSasV1]);
         assert_eq!(
             event.content.timestamp,
-            UInt::new(1_559_598_944_869).unwrap()
+            UNIX_EPOCH + Duration::from_millis(1_559_598_944_869)
         );
     }
 }
diff --git a/tests/ruma_events_macros.rs b/tests/ruma_events_macros.rs
index e1cf116c..a1061e98 100644
--- a/tests/ruma_events_macros.rs
+++ b/tests/ruma_events_macros.rs
@@ -1,6 +1,9 @@
-use std::{collections::HashMap, convert::TryFrom};
+use std::{
+    collections::HashMap,
+    convert::TryFrom,
+    time::{Duration, UNIX_EPOCH},
+};
 
-use js_int::UInt;
 use ruma_events::util::serde_json_eq_try_from_raw;
 use ruma_events_macros::ruma_event;
 use ruma_identifiers::{EventId, RoomAliasId, RoomId, UserId};
@@ -29,7 +32,7 @@ mod common_case {
                 aliases: Vec::with_capacity(0),
             },
             event_id: EventId::try_from("$h29iv0s8:example.com").unwrap(),
-            origin_server_ts: UInt::try_from(1).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1),
             prev_content: None,
             room_id: None,
             sender: UserId::try_from("@carl:example.com").unwrap(),
@@ -56,7 +59,7 @@ mod common_case {
                 aliases: vec![RoomAliasId::try_from("#room:example.org").unwrap()],
             },
             event_id: EventId::try_from("$h29iv0s8:example.com").unwrap(),
-            origin_server_ts: UInt::try_from(1).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1),
             prev_content: Some(AliasesEventContent {
                 aliases: Vec::with_capacity(0),
             }),
@@ -89,7 +92,7 @@ mod common_case {
                 aliases: vec![RoomAliasId::try_from("#room:example.org").unwrap()],
             },
             event_id: EventId::try_from("$h29iv0s8:example.com").unwrap(),
-            origin_server_ts: UInt::try_from(1).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1),
             prev_content: Some(AliasesEventContent {
                 aliases: Vec::with_capacity(0),
             }),
@@ -144,7 +147,7 @@ mod extra_fields {
             content: RedactionEventContent { reason: None },
             redacts: EventId::try_from("$h29iv0s8:example.com").unwrap(),
             event_id: EventId::try_from("$h29iv0s8:example.com").unwrap(),
-            origin_server_ts: UInt::try_from(1).unwrap(),
+            origin_server_ts: UNIX_EPOCH + Duration::from_millis(1),
             room_id: Some(RoomId::try_from("!n8f893n9:example.com").unwrap()),
             sender: UserId::try_from("@carl:example.com").unwrap(),
             unsigned: serde_json::from_str(r#"{"foo":"bar"}"#).unwrap(),