diff --git a/collects/parser-tools/private-yacc/parser-builder.ss b/collects/parser-tools/private-yacc/parser-builder.ss
index ecf8459..0e8e8e2 100644
--- a/collects/parser-tools/private-yacc/parser-builder.ss
+++ b/collects/parser-tools/private-yacc/parser-builder.ss
@@ -118,7 +118,9 @@
                                                       (lambda ()
                                                         ,(if src-pos
                                                              `(err #t (token-name tok) (token-value tok) (cadr ip) (caddr ip))
-                                                             `(err #t (token-name tok) (token-value tok)))))))))
+                                                             `(err #t (token-name tok) (token-value tok)))
+							(raise-read-error (format "parser: got token of unknown type ~a" (token-name tok)))))))))
+								
                (lambda (get-token)
                  (let parsing-loop ((stack (list 0))
 				    (ip (get-token)))
@@ -141,7 +143,7 @@
                                                    ((symbol? ip) (make-token ip #f))
                                                    ((token? ip) ip)
                                                    (else (raise-type-error 'parser "token or symbol" 0 ip)))))
-                          (action (find-action stack tok) ,@(if src-pos `(ip) `())))
+                          (action (find-action stack tok ,@(if src-pos `(ip) `()))))
                      (cond
                        ((shift? action)
                         ;; (printf "shift:~a~n" (shift-state action))