diff --git a/src/Alignment.hs b/src/Alignment.hs
index b5fddd9da..9631451e1 100644
--- a/src/Alignment.hs
+++ b/src/Alignment.hs
@@ -101,7 +101,7 @@ openRange source range = (at source <$> maybeLastIndex range) /= Just '\n'
 -- | A row in a split diff, composed of a before line and an after line.
 type Row a = Both (Line a)
 
-type AlignFunction f = forall b. f [Line b] -> [f (Line b)]
+type AlignFunction f = forall b list. (Align list, Applicative list) => f (list (Line b)) -> list (f (Line b))
 
 -- | Merge open lines and prepend closed lines (as determined by a pair of functions) onto a list of rows.
 adjoinRows :: Applicative f => (f [Line a] -> [f (Line a)]) -> f (Line a) -> [f (Line a)] -> [f (Line a)]