diff --git a/collects/mzlib/functior.ss b/collects/mzlib/functior.ss
index 003fe1a..26b8eff 100644
--- a/collects/mzlib/functior.ss
+++ b/collects/mzlib/functior.ss
@@ -171,7 +171,10 @@
 	 [(f init l) (fold-one f init l)]
 	 [(f init l . ls) (fold-n f init (cons l ls))]))))
    
-   (define first (polymorphic (lambda (x) (car x))))
+   (define first (polymorphic (lambda (x) 
+				(unless (pair? x)
+					(raise-type-error 'first "list" x))
+				(car x))))
    (define second (polymorphic cadr))
    (define third (polymorphic caddr))
    (define fourth (polymorphic cadddr))
@@ -180,8 +183,11 @@
    (define seventh (polymorphic (compose fourth cdddr)))
    (define eighth (polymorphic (compose fourth cddddr)))
 
-   (define rest (polymorphic (lambda (x) (cdr x))))
-
+   (define rest (polymorphic (lambda (x) 
+			       (unless (pair? x)
+				       (raise-type-error 'rest "list" x))
+			       (cdr x))))
+   
    (define  build-string
      (lambda  (n  fcn)
        (unless  (and (integer? n) (exact? n) (>= n 0))