diff --git a/output/js/util.js b/output/js/util.js
index dc17f51..d5d4152 100644
--- a/output/js/util.js
+++ b/output/js/util.js
@@ -11,12 +11,13 @@ class _RoomInfo {
 		const response = await fetch(this.ROOMS_ENDPOINT);
 		const servers = await response.json();
 		for (const server of servers) {
+			const { server_id } = server;
 			for (const room of server.rooms) {
-				const identifier = `${room.token}+${server.pubkey.slice(0, 4)}`;
-				this.rooms[identifier] = {...room, server_key: server.pubkey};
+				const identifier = `${room.token}+${server_id}`;
+				this.rooms[identifier] = {...room, server_id};
 			}
 			delete server.rooms;
-			this.servers[server.pubkey] = server;
+			this.servers[server_id] = server;
 		}
 	}
 
@@ -44,7 +45,7 @@ class _RoomInfo {
 	 */
 	static getRoomServer(identifier) {
 		this.assertRoomExists(identifier);
-		return this.servers[this.rooms[identifier].server_key];
+		return this.servers[this.rooms[identifier].server_id];
 	}
 }
 export class RoomInfo {
diff --git a/php/servers/servers-rooms.php b/php/servers/servers-rooms.php
index 08e06d6..7712c55 100644
--- a/php/servers/servers-rooms.php
+++ b/php/servers/servers-rooms.php
@@ -897,6 +897,7 @@
 			unset($details['merge_error']);
 			unset($details['pubkey_candidates']);
 			$details['pubkey'] = $this->get_pubkey();
+			$details['server_id'] = $this->get_server_id();
 			return $details;
 		}
 
@@ -1155,6 +1156,15 @@
 			return count($this->pubkey_candidates) == 1;
 		}
 
+		/**
+		 * Returns an ID based on the server URL and public key.
+		 */
+		public function get_server_id(): string {
+			$pubkey_prefix = substr($this->get_pubkey(), 0, 4);
+			$hostname_hash_prefix = substr(md5($this->get_hostname(include_port: true)), 0, 4);
+			return $pubkey_prefix . $hostname_hash_prefix;
+		}
+
 		/**
 		 * Returns the room of the given token, or null if one does not exist.
 		 */