diff --git a/php/servers/servers-rooms.php b/php/servers/servers-rooms.php
index 26ce46f..7f2e526 100644
--- a/php/servers/servers-rooms.php
+++ b/php/servers/servers-rooms.php
@@ -678,6 +678,11 @@
 
 				$hostname = url_get_base($base_url, false);
 
+				if (!isset($pubkeys[$hostname])) {
+					log_error("Known server $hostname has no known pubkey.");
+					throw new Error("Known server $hostname has no known pubkey");
+				}
+
 				$server->pubkey = $pubkeys[$hostname];
 
 				$servers[] = $server;