diff --git a/hm.cf b/hm.cf
index a05995e..02a181b 100644
--- a/hm.cf
+++ b/hm.cf
@@ -2,7 +2,7 @@ layout toplevel ;
 
 entrypoints [Def], Exp ;
 
-token Id ((letter|digit|'_'|'['|']')+) ;
+token Id ((letter|digit|["[]_"])+) ;
 
 comment "--" ;
 comment "{-" "-}" ;