diff --git a/Cargo.lock b/Cargo.lock
index 3a1b80f41..6dafff5a5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3540,6 +3540,7 @@ dependencies = [
  "ruma",
  "serde",
  "serde_json",
+ "sha2",
  "tokio",
  "tracing-subscriber",
  "vodozemac",
diff --git a/testing/matrix-sdk-test/Cargo.toml b/testing/matrix-sdk-test/Cargo.toml
index 910f2806c..dfa803d91 100644
--- a/testing/matrix-sdk-test/Cargo.toml
+++ b/testing/matrix-sdk-test/Cargo.toml
@@ -32,6 +32,7 @@ matrix-sdk-test-macros = { version = "0.16.0", path = "../matrix-sdk-test-macros
 ruma = { workspace = true, features = ["client-api-s", "rand", "unstable-msc3381", "unstable-msc4274"] }
 serde.workspace = true
 serde_json.workspace = true
+sha2.workspace = true
 vodozemac.workspace = true
 
 [target.'cfg(not(target_family = "wasm"))'.dependencies]
diff --git a/testing/matrix-sdk-test/src/event_factory.rs b/testing/matrix-sdk-test/src/event_factory.rs
index dc2087ab9..81c728122 100644
--- a/testing/matrix-sdk-test/src/event_factory.rs
+++ b/testing/matrix-sdk-test/src/event_factory.rs
@@ -105,6 +105,8 @@ use ruma::{
 use serde::Serialize;
 use serde_json::json;
 
+use crate::base64_sha256_hash;
+
 pub trait TimestampArg {
     fn to_milliseconds_since_unix_epoch(self) -> MilliSecondsSinceUnixEpoch;
 }
@@ -342,20 +344,6 @@ where
             map.insert("sender".to_owned(), json!(sender));
         }
 
-        if self.format.has_event_id() && !self.no_event_id {
-            let event_id = self.event_id.unwrap_or_else(|| {
-                let server_name = self
-                    .room
-                    .as_ref()
-                    .and_then(|room_id| room_id.server_name())
-                    .unwrap_or(server_name!("dummy.org"));
-
-                EventId::new_v1(server_name)
-            });
-
-            map.insert("event_id".to_owned(), json!(event_id));
-        }
-
         if self.format.has_room_id() {
             let room_id = self.room.expect("TimelineEvent requires a room id");
             map.insert("room_id".to_owned(), json!(room_id));
@@ -365,14 +353,27 @@ where
             map.insert("redacts".to_owned(), json!(redacts));
         }
 
-        if let Some(unsigned) = self.unsigned {
-            map.insert("unsigned".to_owned(), json!(unsigned));
-        }
-
         if let Some(state_key) = self.state_key {
             map.insert("state_key".to_owned(), json!(state_key));
         }
 
+        if self.format.has_event_id() && !self.no_event_id {
+            let event_id = self.event_id.unwrap_or_else(|| {
+                // Compute a hash of the event to use it as the event ID, similar to how a
+                // server would. This is a little bit different since a server would redact the
+                // event before hashing, but at least the event ID construction will be
+                // deterministic and have the same format as in recent room versions.
+                let bytes = serde_json::to_vec(&map).unwrap();
+                EventId::new_v2_or_v3(&base64_sha256_hash(&bytes)).unwrap()
+            });
+
+            map.insert("event_id".to_owned(), json!(event_id));
+        }
+
+        if let Some(unsigned) = self.unsigned {
+            map.insert("unsigned".to_owned(), json!(unsigned));
+        }
+
         json
     }
 
diff --git a/testing/matrix-sdk-test/src/lib.rs b/testing/matrix-sdk-test/src/lib.rs
index 0554c68c4..a7ea6fefd 100644
--- a/testing/matrix-sdk-test/src/lib.rs
+++ b/testing/matrix-sdk-test/src/lib.rs
@@ -5,8 +5,11 @@ pub use matrix_sdk_test_macros::async_test;
 use ruma::{
     RoomId, UserId,
     api::{IncomingResponse, OutgoingResponse},
-    room_id, user_id,
+    room_id,
+    serde::{Base64, base64::UrlSafe},
+    user_id,
 };
+use sha2::{Digest, Sha256};
 
 /// Create a `Raw<AnyMessageLikeEventContent>` from arbitrary JSON.
 ///
@@ -124,3 +127,12 @@ impl<T: fmt::Display + fmt::Debug> From<T> for TestError {
 }
 
 pub type TestResult = Result<(), TestError>;
+
+/// Compute the sha256 hash of the given bytes and convert it to unpadded
+/// URL-safe base64.
+///
+/// This matches the format of event IDs since room version 4, and of room IDs
+/// since room version 12.
+pub fn base64_sha256_hash(bytes: &[u8]) -> String {
+    Base64::<UrlSafe, _>::new(Sha256::digest(bytes)).encode()
+}