diff --git a/linkcheck/bookmarks/safari.py b/linkcheck/bookmarks/safari.py
index 28b3fe72..1c19c966 100644
--- a/linkcheck/bookmarks/safari.py
+++ b/linkcheck/bookmarks/safari.py
@@ -26,6 +26,8 @@ except ImportError:
     has_biplist = False
 
 if sys.version_info >= (3, 9):
+    # Although the biplist module imports on Python 3.9 it is not compatible:
+    # https://bitbucket.org/wooster/biplist/issues/12
     has_biplist = False