diff --git a/src/client_server/membership.rs b/src/client_server/membership.rs
index 38a7e9f9..91472428 100644
--- a/src/client_server/membership.rs
+++ b/src/client_server/membership.rs
@@ -1035,7 +1035,8 @@ pub(crate) async fn invite_helper<'a>(
         let pub_key_map = RwLock::new(BTreeMap::new());
 
         // We do not add the event_id field to the pdu here because of signature and hashes checks
-        let (event_id, value) = match crate::pdu::gen_event_id_canonical_json(&response.event) {
+        let (event_id, value) = match crate::pdu::gen_event_id_canonical_json(&response.event, &db)
+        {
             Ok(t) => t,
             Err(_) => {
                 // Event could not be converted to canonical json
diff --git a/src/database/globals.rs b/src/database/globals.rs
index 0c6476d5..30bf9373 100644
--- a/src/database/globals.rs
+++ b/src/database/globals.rs
@@ -138,7 +138,11 @@ impl Globals {
         // Supported and stable room versions
         let stable_room_versions = vec![RoomVersionId::Version6];
         // Experimental, partially supported room versions
-        let unstable_room_versions = vec![RoomVersionId::Version4, RoomVersionId::Version5];
+        let unstable_room_versions = vec![
+            RoomVersionId::Version3,
+            RoomVersionId::Version4,
+            RoomVersionId::Version5,
+        ];
 
         let s = Self {
             globals,
diff --git a/src/database/rooms.rs b/src/database/rooms.rs
index 338b0895..1b956eb1 100644
--- a/src/database/rooms.rs
+++ b/src/database/rooms.rs
@@ -3451,4 +3451,27 @@ impl Rooms {
 
         Ok(())
     }
+
+    /// Returns the room's version.
+    #[tracing::instrument(skip(self))]
+    pub fn get_room_version(&self, room_id: &RoomId) -> RoomVersionId {
+        let create_event = self
+            .room_state_get(room_id, &EventType::RoomCreate, "")
+            .unwrap();
+
+        let create_event_content: Option<RoomCreateEventContent> = create_event
+            .as_ref()
+            .map(|create_event| {
+                serde_json::from_str(create_event.content.get()).map_err(|e| {
+                    warn!("Invalid create event: {}", e);
+                    Error::bad_database("Invalid create event in db.")
+                })
+            })
+            .transpose()
+            .unwrap();
+
+        create_event_content
+            .map(|create_event| create_event.room_version)
+            .expect("Invalid room version")
+    }
 }
diff --git a/src/pdu.rs b/src/pdu.rs
index 0f99f43b..bcd52edd 100644
--- a/src/pdu.rs
+++ b/src/pdu.rs
@@ -1,4 +1,4 @@
-use crate::Error;
+use crate::{Database, Error};
 use ruma::{
     events::{
         room::member::RoomMemberEventContent, AnyEphemeralRoomEvent, AnyInitialStateEvent,
@@ -6,7 +6,7 @@ use ruma::{
         EventType, StateEvent,
     },
     serde::{CanonicalJsonObject, CanonicalJsonValue, Raw},
-    state_res, EventId, MilliSecondsSinceUnixEpoch, RoomId, RoomVersionId, UInt, UserId,
+    state_res, EventId, MilliSecondsSinceUnixEpoch, RoomId, UInt, UserId,
 };
 use serde::{Deserialize, Serialize};
 use serde_json::{
@@ -331,16 +331,24 @@ impl Ord for PduEvent {
 /// Returns a tuple of the new `EventId` and the PDU as a `BTreeMap<String, CanonicalJsonValue>`.
 pub(crate) fn gen_event_id_canonical_json(
     pdu: &RawJsonValue,
+    db: &Database,
 ) -> crate::Result<(EventId, CanonicalJsonObject)> {
-    let value = serde_json::from_str(pdu.get()).map_err(|e| {
+    let value: CanonicalJsonObject = serde_json::from_str(pdu.get()).map_err(|e| {
         warn!("Error parsing incoming event {:?}: {:?}", pdu, e);
         Error::BadServerResponse("Invalid PDU in server response")
     })?;
 
+    let room_id = value
+        .get("room_id")
+        .and_then(|id| RoomId::try_from(id.as_str()?).ok())
+        .expect("Invalid room id in event");
+
+    let room_version_id = db.rooms.get_room_version(&room_id);
+
     let event_id = EventId::try_from(&*format!(
         "${}",
         // Anything higher than version3 behaves the same
-        ruma::signatures::reference_hash(&value, &RoomVersionId::Version6)
+        ruma::signatures::reference_hash(&value, &room_version_id)
             .expect("ruma can calculate reference hashes")
     ))
     .expect("ruma's reference hashes are valid event ids");
diff --git a/src/server_server.rs b/src/server_server.rs
index 7709f1ea..5357a907 100644
--- a/src/server_server.rs
+++ b/src/server_server.rs
@@ -725,7 +725,7 @@ pub async fn send_transaction_message_route(
 
     for pdu in &body.pdus {
         // We do not add the event_id field to the pdu here because of signature and hashes checks
-        let (event_id, value) = match crate::pdu::gen_event_id_canonical_json(pdu) {
+        let (event_id, value) = match crate::pdu::gen_event_id_canonical_json(pdu, &db) {
             Ok(t) => t,
             Err(_) => {
                 // Event could not be converted to canonical json
@@ -1911,7 +1911,7 @@ pub(crate) fn fetch_and_handle_outliers<'a>(
                         Ok(res) => {
                             warn!("Got {} over federation", id);
                             let (calculated_event_id, value) =
-                                match crate::pdu::gen_event_id_canonical_json(&res.pdu) {
+                                match crate::pdu::gen_event_id_canonical_json(&res.pdu, &db) {
                                     Ok(t) => t,
                                     Err(_) => {
                                         back_off((**id).clone());
@@ -2815,7 +2815,7 @@ async fn create_join_event(
     // let mut auth_cache = EventMap::new();
 
     // We do not add the event_id field to the pdu here because of signature and hashes checks
-    let (event_id, value) = match crate::pdu::gen_event_id_canonical_json(pdu) {
+    let (event_id, value) = match crate::pdu::gen_event_id_canonical_json(pdu, &db) {
         Ok(t) => t,
         Err(_) => {
             // Event could not be converted to canonical json