diff --git a/grammar/SIPGrammar.st b/grammar/SIPGrammar.st
index 9c6c55c..90d030e 100644
--- a/grammar/SIPGrammar.st
+++ b/grammar/SIPGrammar.st
@@ -670,9 +670,9 @@ PP.PPCompositeParser subclass: SIPGrammar [
     token [
         <category: 'generic'>
 
-        ^ (#letter asParser /
-            (PP.PPPredicateObjectParser chars: '0123456789-.!%*_+`''~' message: 'token'))
-            plus flatten
+        ^ (PP.PPPredicateObjectParser on: (PP.PPCharSetPredicate on:
+                                [:char | char isAlphaNumeric or: [
+                                    '-.!%*_+`''~' includes: char]]) message: 'token') plus flatten
     ]
 
     header_name [