diff --git a/tests/haskell-mode-tests.el b/tests/haskell-mode-tests.el
index 2d17b1517..078c246e7 100644
--- a/tests/haskell-mode-tests.el
+++ b/tests/haskell-mode-tests.el
@@ -372,4 +372,17 @@ Also should respect 10 column fill."
 		"--f g h"
 		"        --            i j")))
 
+(ert-deftest fill-comment-haddock-1 ()
+  (check-fill '("-- | a b c"
+                "-- d")
+	      '("-- @| a b c d")))
+
+(ert-deftest fill-comment-haddock-2 ()
+  ;; FIXME: This shouldn't be failing, https://github.com/haskell/haskell-mode/issues/851.
+  :expected-result :failed
+  (check-fill '("-- | a b c"
+                "-- d e")
+	      '("-- @| a b c d"
+                "-- e")))
+
 (provide 'haskell-mode-tests)