diff --git a/src/Sudoku.hs b/src/Sudoku.hs
index 9bcd3ef..576ff71 100644
--- a/src/Sudoku.hs
+++ b/src/Sudoku.hs
@@ -113,11 +113,11 @@ nextGrids grid =
 solve :: Grid -> Maybe Grid
 solve grid = pruneGrid grid >>= solve'
   where
-    solve' grid'
-      | isGridInvalid grid = Nothing
-      | isGridFilled grid' = Just grid'
-      | otherwise          =
-          let (grid1, grid2) = nextGrids grid'
+    solve' g
+      | isGridInvalid g = Nothing
+      | isGridFilled g  = Just g
+      | otherwise       =
+          let (grid1, grid2) = nextGrids g
           in solve grid1 <|> solve grid2
 
 main :: IO ()