From 67d8d72506a800e582a8062c011c3316fc5cef5a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=A9=C5=BAera?= <ezera@polymerheat.com>
Date: Thu, 26 Mar 2026 18:52:03 -0500
Subject: [PATCH] fix: return 404 when joining non-existent room

Fixes #1443.
---
 changelog.d/1579.bugfix           | 1 +
 src/api/client/membership/join.rs | 9 +++++++++
 src/core/error/err.rs             | 8 ++++++++
 3 files changed, 18 insertions(+)
 create mode 100644 changelog.d/1579.bugfix

diff --git a/changelog.d/1579.bugfix b/changelog.d/1579.bugfix
new file mode 100644
index 000000000..5160a2a6e
--- /dev/null
+++ b/changelog.d/1579.bugfix
@@ -0,0 +1 @@
+Fixed error 500 when joining non-existent rooms. Contributed by @ezera.
diff --git a/src/api/client/membership/join.rs b/src/api/client/membership/join.rs
index cbb825068..4c3a53d02 100644
--- a/src/api/client/membership/join.rs
+++ b/src/api/client/membership/join.rs
@@ -785,6 +785,15 @@ async fn join_room_by_id_helper_local(
 	};
 
 	if servers.is_empty() || servers.len() == 1 && services.globals.server_is_ours(&servers[0]) {
+		if !services.rooms.metadata.exists(room_id).await {
+			return Err!(Request(
+				Unknown(
+					"Room was not found locally and no servers were found to help us discover it"
+				),
+				NOT_FOUND
+			));
+		}
+
 		return Err(error);
 	}
 
diff --git a/src/core/error/err.rs b/src/core/error/err.rs
index 314e03f3a..39f6e33fe 100644
--- a/src/core/error/err.rs
+++ b/src/core/error/err.rs
@@ -77,6 +77,14 @@ macro_rules! err {
 		)
 	};
 
+	(Request($variant:ident($($args:tt)+), $status_code:ident)) => {
+		$crate::error::Error::Request(
+			$crate::ruma::api::client::error::ErrorKind::$variant,
+			$crate::format_maybe!($($args)+),
+			$crate::http::StatusCode::$status_code,
+		)
+	};
+
 	(Config($item:literal, $($args:tt)+)) => {{
 		let mut buf = String::new();
 		$crate::error::Error::Config($item, $crate::err_log!(buf, error, config = %$item, $($args)+))