diff --git a/hs/aoc2024.cabal b/hs/aoc2024.cabal
index f77b94ea..1bc53a88 100644
--- a/hs/aoc2024.cabal
+++ b/hs/aoc2024.cabal
@@ -32,6 +32,7 @@ library
     base ^>=4.20.0.0,
     containers ^>=0.7,
     megaparsec ^>=9.7.0,
+    mtl ^>=2.3.1,
     parser-combinators ^>=1.3.0,
     text ^>=2.1.1,
 
@@ -63,6 +64,7 @@ test-suite aoc2024-test
   other-modules:
     Day1Spec
     Day2Spec
+    Day3Spec
 
   build-depends:
     aoc2024,
diff --git a/hs/src/Day3.hs b/hs/src/Day3.hs
index 367790a1..af9034d8 100644
--- a/hs/src/Day3.hs
+++ b/hs/src/Day3.hs
@@ -1,10 +1,11 @@
-{-# LANGUAGE OverloadedStrings #-}
-
 -- |
 -- Module:         Day3
 -- Description:    <https://adventofcode.com/2024/day/3 Day 3: Mull It Over>
 module Day3 (part1, part2) where
 
+import Control.Monad (filterM)
+import Control.Monad.State (MonadState (get, put), evalState)
+import Data.Either (rights)
 import Data.Functor (($>))
 import Data.String (IsString)
 import Data.Text (Text)
@@ -26,8 +27,4 @@ part1 :: Text -> Either (ParseErrorBundle Text Void) Int
 part1 = fmap sum . parse parser1 ""
 
 part2 :: Text -> Either (ParseErrorBundle Text Void) Int
-part2 = fmap (snd . foldl' go (True, 0)) . parse parser2 ""
-  where
-    go (_, a) (Left z) = (z, a)
-    go (True, a) (Right b) = (True,) $! a + b
-    go k _ = k
+part2 = fmap (sum . rights . flip evalState True . filterM (either (($> False) . put) $ const get)) . parse parser2 ""