diff --git a/exercises/Set4b.hs b/exercises/Set4b.hs
index ef5fb12..83b640b 100644
--- a/exercises/Set4b.hs
+++ b/exercises/Set4b.hs
@@ -38,7 +38,8 @@ myMaximum :: [Int] -> Int
 myMaximum [] = 0
 myMaximum (x:xs) = foldr maxHelper x xs
 
-maxHelper = todo
+maxHelper :: Int -> Int -> Int
+maxHelper x acc = if x > acc then x else acc
 
 ------------------------------------------------------------------------------
 -- Ex 3: compute the sum and length of a list with a fold. Define