diff --git a/Cabal-syntax/src/Language/Haskell/Extension.hs b/Cabal-syntax/src/Language/Haskell/Extension.hs
index 50b720219e7..dce34560586 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
   | -- | Allow use of or-pattern syntax, condensing multiple patterns
     -- into a single one.