diff --git a/crates/ruma-common/src/events/audio.rs b/crates/ruma-common/src/events/audio.rs
index dc044036..26b1bb33 100644
--- a/crates/ruma-common/src/events/audio.rs
+++ b/crates/ruma-common/src/events/audio.rs
@@ -40,7 +40,7 @@ pub struct AudioEventContent {
 
     /// Information about related messages.
     #[serde(flatten, skip_serializing_if = "Option::is_none")]
-    pub relates_to: Option<Relation>,
+    pub relates_to: Option<Relation<AudioEventContentWithoutRelation>>,
 }
 
 impl AudioEventContent {
diff --git a/crates/ruma-common/src/events/emote.rs b/crates/ruma-common/src/events/emote.rs
index 9725e374..5f87f66f 100644
--- a/crates/ruma-common/src/events/emote.rs
+++ b/crates/ruma-common/src/events/emote.rs
@@ -24,7 +24,7 @@ pub struct EmoteEventContent {
 
     /// Information about related messages.
     #[serde(flatten, skip_serializing_if = "Option::is_none")]
-    pub relates_to: Option<Relation>,
+    pub relates_to: Option<Relation<EmoteEventContentWithoutRelation>>,
 }
 
 impl EmoteEventContent {
diff --git a/crates/ruma-common/src/events/file.rs b/crates/ruma-common/src/events/file.rs
index b9c9b3d0..0a95c56f 100644
--- a/crates/ruma-common/src/events/file.rs
+++ b/crates/ruma-common/src/events/file.rs
@@ -35,7 +35,7 @@ pub struct FileEventContent {
 
     /// Information about related messages.
     #[serde(flatten, skip_serializing_if = "Option::is_none")]
-    pub relates_to: Option<Relation>,
+    pub relates_to: Option<Relation<FileEventContentWithoutRelation>>,
 }
 
 impl FileEventContent {
diff --git a/crates/ruma-common/src/events/image.rs b/crates/ruma-common/src/events/image.rs
index 61004125..03124f16 100644
--- a/crates/ruma-common/src/events/image.rs
+++ b/crates/ruma-common/src/events/image.rs
@@ -51,7 +51,7 @@ pub struct ImageEventContent {
 
     /// Information about related messages.
     #[serde(flatten, skip_serializing_if = "Option::is_none")]
-    pub relates_to: Option<Relation>,
+    pub relates_to: Option<Relation<ImageEventContentWithoutRelation>>,
 }
 
 impl ImageEventContent {
diff --git a/crates/ruma-common/src/events/location.rs b/crates/ruma-common/src/events/location.rs
index 60dd52ae..c7e180dd 100644
--- a/crates/ruma-common/src/events/location.rs
+++ b/crates/ruma-common/src/events/location.rs
@@ -40,7 +40,7 @@ pub struct LocationEventContent {
 
     /// Information about related messages.
     #[serde(flatten, skip_serializing_if = "Option::is_none")]
-    pub relates_to: Option<Relation>,
+    pub relates_to: Option<Relation<LocationEventContentWithoutRelation>>,
 }
 
 impl LocationEventContent {
diff --git a/crates/ruma-common/src/events/message.rs b/crates/ruma-common/src/events/message.rs
index b6925e00..7c129790 100644
--- a/crates/ruma-common/src/events/message.rs
+++ b/crates/ruma-common/src/events/message.rs
@@ -73,7 +73,7 @@ pub struct MessageEventContent {
 
     /// Information about related messages.
     #[serde(flatten, skip_serializing_if = "Option::is_none")]
-    pub relates_to: Option<Relation>,
+    pub relates_to: Option<Relation<MessageEventContentWithoutRelation>>,
 }
 
 impl MessageEventContent {
diff --git a/crates/ruma-common/src/events/notice.rs b/crates/ruma-common/src/events/notice.rs
index f6e4ab25..f593ef9b 100644
--- a/crates/ruma-common/src/events/notice.rs
+++ b/crates/ruma-common/src/events/notice.rs
@@ -24,7 +24,7 @@ pub struct NoticeEventContent {
 
     /// Information about related messages.
     #[serde(flatten, skip_serializing_if = "Option::is_none")]
-    pub relates_to: Option<Relation>,
+    pub relates_to: Option<Relation<NoticeEventContentWithoutRelation>>,
 }
 
 impl NoticeEventContent {
diff --git a/crates/ruma-common/src/events/room/encrypted.rs b/crates/ruma-common/src/events/room/encrypted.rs
index c2c98d7f..fd034a2b 100644
--- a/crates/ruma-common/src/events/room/encrypted.rs
+++ b/crates/ruma-common/src/events/room/encrypted.rs
@@ -107,8 +107,8 @@ pub enum Relation {
     _Custom,
 }
 
-impl From<message::Relation> for Relation {
-    fn from(rel: message::Relation) -> Self {
+impl<C> From<message::Relation<C>> for Relation {
+    fn from(rel: message::Relation<C>) -> Self {
         match rel {
             message::Relation::Reply { in_reply_to } => Self::Reply { in_reply_to },
             message::Relation::Replacement(re) => {
diff --git a/crates/ruma-common/src/events/room/message.rs b/crates/ruma-common/src/events/room/message.rs
index 20d278ed..21816aeb 100644
--- a/crates/ruma-common/src/events/room/message.rs
+++ b/crates/ruma-common/src/events/room/message.rs
@@ -62,7 +62,7 @@ pub struct RoomMessageEventContent {
     ///
     /// [rich replies]: https://spec.matrix.org/v1.2/client-server-api/#rich-replies
     #[serde(flatten, skip_serializing_if = "Option::is_none")]
-    pub relates_to: Option<Relation>,
+    pub relates_to: Option<Relation<MessageType>>,
 }
 
 impl RoomMessageEventContent {
@@ -467,7 +467,7 @@ impl From<RoomMessageEventContent> for MessageType {
 #[derive(Clone, Debug)]
 #[allow(clippy::manual_non_exhaustive)]
 #[cfg_attr(not(feature = "unstable-exhaustive-types"), non_exhaustive)]
-pub enum Relation {
+pub enum Relation<C> {
     /// An `m.in_reply_to` relation indicating that the event is a reply to another event.
     Reply {
         /// Information about another message being replied to.
@@ -475,7 +475,7 @@ pub enum Relation {
     },
 
     /// An event that replaces another event.
-    Replacement(Replacement),
+    Replacement(Replacement<C>),
 
     /// An event that belongs to a thread.
     Thread(Thread),
@@ -504,17 +504,17 @@ impl InReplyTo {
 /// [replaces another event]: https://spec.matrix.org/v1.4/client-server-api/#event-replacements
 #[derive(Clone, Debug)]
 #[cfg_attr(not(feature = "unstable-exhaustive-types"), non_exhaustive)]
-pub struct Replacement {
+pub struct Replacement<C> {
     /// The ID of the event being replaced.
     pub event_id: OwnedEventId,
 
     /// New content.
-    pub new_content: Box<RoomMessageEventContent>,
+    pub new_content: C,
 }
 
-impl Replacement {
+impl<C> Replacement<C> {
     /// Creates a new `Replacement` with the given event ID and new content.
-    pub fn new(event_id: OwnedEventId, new_content: Box<RoomMessageEventContent>) -> Self {
+    pub fn new(event_id: OwnedEventId, new_content: C) -> Self {
         Self { event_id, new_content }
     }
 }
diff --git a/crates/ruma-common/src/events/room/message/content_serde.rs b/crates/ruma-common/src/events/room/message/content_serde.rs
index 7ca61cee..fe0b1ccb 100644
--- a/crates/ruma-common/src/events/room/message/content_serde.rs
+++ b/crates/ruma-common/src/events/room/message/content_serde.rs
@@ -47,8 +47,8 @@ impl<'de> Deserialize<'de> for RoomMessageEventContent {
     {
         let json = Box::<RawJsonValue>::deserialize(deserializer)?;
         let mut deserializer = serde_json::Deserializer::from_str(json.get());
-        let relates_to =
-            Option::<Relation>::deserialize(&mut deserializer).map_err(de::Error::custom)?;
+        let relates_to = Option::<Relation<MessageType>>::deserialize(&mut deserializer)
+            .map_err(de::Error::custom)?;
 
         Ok(Self { msgtype: from_raw_json_value(&json)?, relates_to })
     }
diff --git a/crates/ruma-common/src/events/room/message/relation_serde.rs b/crates/ruma-common/src/events/room/message/relation_serde.rs
index 2953adeb..ce0dfb5d 100644
--- a/crates/ruma-common/src/events/room/message/relation_serde.rs
+++ b/crates/ruma-common/src/events/room/message/relation_serde.rs
@@ -1,9 +1,12 @@
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
 
-use super::{InReplyTo, Relation, Replacement, RoomMessageEventContent, Thread};
+use super::{InReplyTo, Relation, Replacement, Thread};
 use crate::OwnedEventId;
 
-impl<'de> Deserialize<'de> for Relation {
+impl<'de, C> Deserialize<'de> for Relation<C>
+where
+    C: Deserialize<'de>,
+{
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
         D: Deserializer<'de>,
@@ -47,17 +50,22 @@ impl<'de> Deserialize<'de> for Relation {
     }
 }
 
-impl Serialize for Relation {
+impl<C> Serialize for Relation<C>
+where
+    C: Clone + Serialize,
+{
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
         S: Serializer,
     {
         #[allow(clippy::needless_update)]
         let json_repr = match self {
-            Relation::Reply { in_reply_to } => EventWithRelatesToJsonRepr::new(RelatesToJsonRepr {
-                in_reply_to: Some(in_reply_to.clone()),
-                ..Default::default()
-            }),
+            Relation::Reply { in_reply_to } => {
+                EventWithRelatesToJsonRepr::<C>::new(RelatesToJsonRepr {
+                    in_reply_to: Some(in_reply_to.clone()),
+                    ..Default::default()
+                })
+            }
             Relation::Replacement(Replacement { event_id, new_content }) => {
                 EventWithRelatesToJsonRepr {
                     relates_to: RelatesToJsonRepr {
@@ -79,28 +87,34 @@ impl Serialize for Relation {
                     ..Default::default()
                 })
             }
-            Relation::_Custom => EventWithRelatesToJsonRepr::default(),
+            Relation::_Custom => EventWithRelatesToJsonRepr::<C>::default(),
         };
 
         json_repr.serialize(serializer)
     }
 }
 
-#[derive(Default, Deserialize, Serialize)]
-struct EventWithRelatesToJsonRepr {
+#[derive(Deserialize, Serialize)]
+struct EventWithRelatesToJsonRepr<C> {
     #[serde(rename = "m.relates_to", default, skip_serializing_if = "RelatesToJsonRepr::is_empty")]
     relates_to: RelatesToJsonRepr,
 
     #[serde(rename = "m.new_content", skip_serializing_if = "Option::is_none")]
-    new_content: Option<Box<RoomMessageEventContent>>,
+    new_content: Option<C>,
 }
 
-impl EventWithRelatesToJsonRepr {
+impl<C> EventWithRelatesToJsonRepr<C> {
     fn new(relates_to: RelatesToJsonRepr) -> Self {
         Self { relates_to, new_content: None }
     }
 }
 
+impl<C> Default for EventWithRelatesToJsonRepr<C> {
+    fn default() -> Self {
+        Self { relates_to: RelatesToJsonRepr::default(), new_content: None }
+    }
+}
+
 /// Struct modeling the different ways relationships can be expressed in a `m.relates_to` field of
 /// an event.
 #[derive(Default, Deserialize, Serialize)]
diff --git a/crates/ruma-common/src/events/video.rs b/crates/ruma-common/src/events/video.rs
index 90777574..f3c3cf69 100644
--- a/crates/ruma-common/src/events/video.rs
+++ b/crates/ruma-common/src/events/video.rs
@@ -50,7 +50,7 @@ pub struct VideoEventContent {
 
     /// Information about related messages.
     #[serde(flatten, skip_serializing_if = "Option::is_none")]
-    pub relates_to: Option<Relation>,
+    pub relates_to: Option<Relation<VideoEventContentWithoutRelation>>,
 }
 
 impl VideoEventContent {
diff --git a/crates/ruma-common/src/events/voice.rs b/crates/ruma-common/src/events/voice.rs
index 2822fbd7..2d5b824c 100644
--- a/crates/ruma-common/src/events/voice.rs
+++ b/crates/ruma-common/src/events/voice.rs
@@ -38,7 +38,7 @@ pub struct VoiceEventContent {
 
     /// Information about related messages.
     #[serde(flatten, skip_serializing_if = "Option::is_none")]
-    pub relates_to: Option<Relation>,
+    pub relates_to: Option<Relation<VoiceEventContentWithoutRelation>>,
 }
 
 impl VoiceEventContent {
diff --git a/crates/ruma-common/tests/events/relations.rs b/crates/ruma-common/tests/events/relations.rs
index ff153c9a..ec7dced6 100644
--- a/crates/ruma-common/tests/events/relations.rs
+++ b/crates/ruma-common/tests/events/relations.rs
@@ -75,7 +75,7 @@ fn replacement_serialize() {
             relates_to: Some(Relation::Replacement(
                 Replacement::new(
                     event_id!("$1598361704261elfgc").to_owned(),
-                    Box::new(RoomMessageEventContent::text_plain("This is the new content.")),
+                    RoomMessageEventContent::text_plain("This is the new content.").into(),
                 )
             ))
         }
@@ -142,7 +142,7 @@ fn replacement_deserialize() {
         }) => replacement
     );
     assert_eq!(replacement.event_id, "$1598361704261elfgc");
-    let text = assert_matches!(replacement.new_content.msgtype, MessageType::Text(text) => text);
+    let text = assert_matches!(replacement.new_content, MessageType::Text(text) => text);
     assert_eq!(text.body, "Hello! My name is bar");
 }
 
diff --git a/crates/ruma-common/tests/events/without_relation.rs b/crates/ruma-common/tests/events/without_relation.rs
index 33998ad7..1d828edd 100644
--- a/crates/ruma-common/tests/events/without_relation.rs
+++ b/crates/ruma-common/tests/events/without_relation.rs
@@ -1,10 +1,7 @@
 use assert_matches::assert_matches;
 use ruma_common::{
     event_id,
-    events::room::message::{
-        InReplyTo, MessageType, Relation, RoomMessageEventContent,
-        RoomMessageEventContentWithoutRelation,
-    },
+    events::room::message::{InReplyTo, MessageType, Relation, RoomMessageEventContent},
 };
 use serde_json::{from_value as from_json_value, json, to_value as to_json_value};
 
@@ -13,7 +10,7 @@ fn serialize_room_message_content_without_relation() {
     let mut content = RoomMessageEventContent::text_plain("Hello, world!");
     content.relates_to =
         Some(Relation::Reply { in_reply_to: InReplyTo::new(event_id!("$eventId").to_owned()) });
-    let without_relation = RoomMessageEventContentWithoutRelation::from(content);
+    let without_relation = MessageType::from(content);
 
     #[cfg(not(feature = "unstable-msc3246"))]
     assert_eq!(
@@ -43,8 +40,8 @@ fn deserialize_room_message_content_without_relation() {
     });
 
     let text = assert_matches!(
-        from_json_value::<RoomMessageEventContentWithoutRelation>(json_data),
-        Ok(RoomMessageEventContentWithoutRelation::Text(text)) => text
+        from_json_value::<MessageType>(json_data),
+        Ok(MessageType::Text(text)) => text
     );
     assert_eq!(text.body, "Hello, world!");
 }
@@ -54,8 +51,7 @@ fn convert_room_message_content_without_relation_to_full() {
     let mut content = RoomMessageEventContent::text_plain("Hello, world!");
     content.relates_to =
         Some(Relation::Reply { in_reply_to: InReplyTo::new(event_id!("$eventId").to_owned()) });
-    let new_content =
-        RoomMessageEventContent::from(RoomMessageEventContentWithoutRelation::from(content));
+    let new_content = RoomMessageEventContent::from(MessageType::from(content));
 
     let (text, relates_to) = assert_matches!(
         new_content,