diff --git a/lasio/las.py b/lasio/las.py
index f414113a..3b6be59f 100644
--- a/lasio/las.py
+++ b/lasio/las.py
@@ -863,6 +863,10 @@ def json(self):
         return self.to_json()
 
     def to_json_old(self):
+        """
+        deprecated: to_json_old version=0.25.1 since=20200507 remove=20210508
+        replacement_options: to_json()
+        """
         obj = OrderedDict()
         for name, section in self.sections.items():
             try: