diff --git a/mad/fib.mad b/mad/fib.mad
index f093016..5318a14 100644
--- a/mad/fib.mad
+++ b/mad/fib.mad
@@ -4,8 +4,9 @@
 (def slowFib (fn (n) (if (< n 2) n (+ (slowFib (- n 1)) (slowFib (- n 2))))))
 
 ;; Return the sum of the last 2 numbers in a sequence
-(def sumOfLast (fn (l) (+ (last l) (get l (- (len l) 2)))))
+(def sumOfLast (fn (l) (+ (last l) (penult l))))
 
 ;; Faster version, return vector of n numbers, tail call optimized
 (def fibListRec (fn (n l) (if (< (len l) n) (fibListRec n (push l (sumOfLast l))) l)))
 (def fibList (fn (n) (fibListRec n [0 1])))
+(def fastFib (fn (n) (sumOfLast (fibList n))))