diff --git a/Cabal-syntax/src/Language/Haskell/Extension.hs b/Cabal-syntax/src/Language/Haskell/Extension.hs
index f9b9324c8f4..a4e96a9d2b7 100644
--- a/Cabal-syntax/src/Language/Haskell/Extension.hs
+++ b/Cabal-syntax/src/Language/Haskell/Extension.hs
@@ -551,7 +551,7 @@ data KnownExtension
   | -- | Allow the use of built-in syntax for list, tuple and sum type constructors
     -- rather than being exclusive to data constructors.
     ListTuplePuns
-  | -- | Support multiline strings
+  | -- | Support multiline strings.
     MultilineStrings
   | -- | Generalises `default` for classes other than `Num`.
     NamedDefaults