--- a/mod_firewall/actions.lib.lua	Thu Jun 08 16:53:12 2023 +0100
+++ b/mod_firewall/actions.lib.lua	Thu Jun 08 16:59:22 2023 +0100
@@ -225,7 +225,7 @@
 				mark = %q;
 				timestamp = current_timestamp;
 			});
-		]]):format(idsafe(name)), { "timestamp" };
+		]]):format(assert(idsafe(name), "Invalid characters in mark name: "..name)), { "timestamp" };
 end
 
 function action_handlers.UNMARK_USER(name)
@@ -233,7 +233,7 @@
 				username = session.username;
 				mark = %q;
 			});
-		]]):format(idsafe(name));
+		]]):format(assert(idsafe(name), "Invalid characters in mark name: "..name));
 end
 
 function action_handlers.ADD_TO(spec)