diff --git a/src/core/matrix/state_res/event_auth.rs b/src/core/matrix/state_res/event_auth.rs
index 759ab5cb..0726b00a 100644
--- a/src/core/matrix/state_res/event_auth.rs
+++ b/src/core/matrix/state_res/event_auth.rs
@@ -13,6 +13,7 @@ use ruma::{
 		power_levels::RoomPowerLevelsEventContent,
 		third_party_invite::RoomThirdPartyInviteEventContent,
 	},
+	EventId,
 	int,
 	serde::{Base64, Raw},
 };
@@ -21,7 +22,6 @@ use serde::{
 	de::{Error as _, IgnoredAny},
 };
 use serde_json::{from_str as from_json_str, value::RawValue as RawJsonValue};
-
 use super::{
 	Error, Event, Result, StateEventType, StateKey, TimelineEventType,
 	power_levels::{
@@ -217,8 +217,9 @@ where
 	}
 
 	/*
-	// TODO: In the past this code caused problems federating with synapse, maybe this has been
-	// resolved already. Needs testing.
+	// TODO: In the past this code was commented as it caused problems with Synapse. This is no
+	// longer the case. This needs to be implemented.
+	// See also: https://github.com/ruma/ruma/pull/2064
 	//
 	// 2. Reject if auth_events
 	// a. auth_events cannot have duplicate keys since it's a BTree
@@ -250,11 +251,33 @@ where
 
 	let room_create_event = match room_create_event {
 		| None => {
-			warn!("no m.room.create event in auth chain");
+			error!(
+				create_event = room_create_event.as_ref().map(Event::event_id).unwrap_or(<&EventId>::try_from("$unknown").unwrap()).as_str(),
+				power_levels = power_levels_event.as_ref().map(Event::event_id).unwrap_or(<&EventId>::try_from("$unknown").unwrap()).as_str(),
+				member_event = sender_member_event.as_ref().map(Event::event_id).unwrap_or(<&EventId>::try_from("$unknown").unwrap()).as_str(),
+				"no m.room.create event found for {} ({})!",
+				incoming_event.event_id().as_str(),
+				incoming_event.room_id().as_str()
+			);
 			return Ok(false);
 		},
 		| Some(e) => e,
 	};
+	// just re-check 1.2 to work around a bug
+	let Some(room_id_server_name) = incoming_event.room_id().server_name() else {
+		warn!("room ID has no servername");
+		return Ok(false);
+	};
+
+	if room_id_server_name != room_create_event.sender().server_name() {
+		warn!(
+			"servername of room ID origin ({}) does not match servername of m.room.create \
+			 sender ({})",
+			room_id_server_name,
+			room_create_event.sender().server_name()
+		);
+		return Ok(false);
+	}
 
 	// 3. If event does not have m.room.create in auth_events reject
 	if !incoming_event
diff --git a/src/core/matrix/state_res/mod.rs b/src/core/matrix/state_res/mod.rs
index 651f6130..a2052b92 100644
--- a/src/core/matrix/state_res/mod.rs
+++ b/src/core/matrix/state_res/mod.rs
@@ -726,8 +726,12 @@ where
 	Fut: Future<Output = Option<E>> + Send,
 	E: Event + Send + Sync,
 {
+	let mut room_id = None;
 	while let Some(sort_ev) = event {
 		debug!(event_id = sort_ev.event_id().as_str(), "mainline");
+		if room_id.is_none() {
+			room_id = Some(sort_ev.room_id().to_owned());
+		}
 
 		let id = sort_ev.event_id();
 		if let Some(depth) = mainline_map.get(id) {
@@ -746,7 +750,7 @@ where
 			}
 		}
 	}
-	// Did not find a power level event so we default to zero
+	warn!("could not find a power event in the mainline map for {room_id:?}, defaulting to zero depth");
 	Ok(0)
 }
 
diff --git a/src/service/rooms/event_handler/handle_outlier_pdu.rs b/src/service/rooms/event_handler/handle_outlier_pdu.rs
index 5339249d..f9889d58 100644
--- a/src/service/rooms/event_handler/handle_outlier_pdu.rs
+++ b/src/service/rooms/event_handler/handle_outlier_pdu.rs
@@ -119,10 +119,7 @@ pub(super) async fn handle_outlier_pdu<'a>(
 	}
 
 	// The original create event must be in the auth events
-	if !matches!(
-		auth_events.get(&(StateEventType::RoomCreate, String::new().into())),
-		Some(_) | None
-	) {
+	if !auth_events.contains_key(&(StateEventType::RoomCreate, String::new().into())) {
 		return Err!(Request(InvalidParam("Incoming event refers to wrong create event.")));
 	}
 
diff --git a/src/service/rooms/timeline/mod.rs b/src/service/rooms/timeline/mod.rs
index e65ae2c7..74c7348d 100644
--- a/src/service/rooms/timeline/mod.rs
+++ b/src/service/rooms/timeline/mod.rs
@@ -698,6 +698,20 @@ impl Service {
 			.await
 			.saturating_add(uint!(1));
 
+		if state_key.is_none() {
+			if prev_events.is_empty() {
+				warn!("Timeline event had zero prev_events, something broke.");
+				return Err!(Request(Unknown("Timeline event had zero prev_events.")));
+			}
+			if depth.le(&uint!(2)) {
+				warn!(
+					"Had unsafe depth of {depth} in {room_id} when creating non-state event. \
+					 Bad!"
+				);
+				return Err!(Request(Unknown("Unsafe depth for non-state event.")));
+			}
+		};
+
 		let mut unsigned = unsigned.unwrap_or_default();
 
 		if let Some(state_key) = &state_key {