diff --git a/largest-series-product/example.hs b/largest-series-product/example.hs
index 861dc372e..f11d05df0 100644
--- a/largest-series-product/example.hs
+++ b/largest-series-product/example.hs
@@ -9,7 +9,7 @@ slices :: Integral a => Int -> String -> [[a]]
 slices n = go . digits
   where go xs = map (take n) $ take (length xs - pred n) (tails xs)
 
-largestProduct :: Integral a => Int -> String -> a
+largestProduct :: Integral a => Int -> String -> Maybe a
 largestProduct n text = case map product (slices n text) of
-  []       -> 1
-  products -> maximum products
+  []       -> Nothing
+  products -> Just $ maximum products
diff --git a/largest-series-product/largest-series-product_test.hs b/largest-series-product/largest-series-product_test.hs
index 2ca8dc9ad..88362aaf8 100644
--- a/largest-series-product/largest-series-product_test.hs
+++ b/largest-series-product/largest-series-product_test.hs
@@ -18,8 +18,11 @@ main = exitProperly $ runTestTT $ TestList
 ints :: [Int] -> [Int]
 ints = id
 
-int :: Int -> Int
-int = id
+int :: Int -> Maybe Int
+int = Just
+
+intNothing :: Maybe Int
+intNothing = Nothing
 
 seriesTests :: [Test]
 seriesTests = map TestCase
@@ -43,8 +46,10 @@ seriesTests = map TestCase
   , int 28350 @=?
     largestProduct 6 "52677741234314237566414902593461595376319419139427"
   , int 1 @=? largestProduct 0 ""
-    -- unlike the Ruby implementation, no error is expected for too small input
-  , int 1 @=? largestProduct 4 "123"
-    -- edge case :)
+  , int 1 @=? largestProduct 0 "123"
+  , intNothing @=? largestProduct 1 ""
+  , intNothing @=? largestProduct 4 "123"
+    -- if all spans contain zero, result is zero.
+  , int 0 @=? largestProduct 3 "99099"
   , int 0 @=? largestProduct 2 "00"
   ]