diff --git a/day4/day4.hs b/day4/day4.hs
index e219db0..a3a297c 100644
--- a/day4/day4.hs
+++ b/day4/day4.hs
@@ -3,6 +3,7 @@ import AoC
 import Control.Applicative ((<|>))
 import Control.Monad (guard, mfilter)
 import Data.Char (isDigit)
+import Data.List (intercalate)
 import Data.Maybe (mapMaybe)
 import Text.ParserCombinators.ReadP
 import Text.Read (readMaybe)