diff --git a/chatmastermind/commands/hist.py b/chatmastermind/commands/hist.py
index 5b14bd2..09cf0ce 100644
--- a/chatmastermind/commands/hist.py
+++ b/chatmastermind/commands/hist.py
@@ -2,7 +2,26 @@ import argparse
 from pathlib import Path
 from ..configuration import Config
 from ..chat import ChatDB
-from ..message import MessageFilter
+from ..message import MessageFilter, Message
+
+
+msg_suffix = Message.file_suffix_write
+
+
+def convert(args: argparse.Namespace, config: Config) -> None:
+    """
+    Convert messages to a new format. Also used to change the suffix,
+    to the latest default message file suffix.
+    """
+    chat = ChatDB.from_dir(Path(config.cache),
+                           Path(config.db))
+    # read all known message files
+    msgs = chat.msg_gather(loc='disk', glob='*.*')
+    # make a set of all message IDs
+    # msg_ids = set([m.msg_id() for m in msgs])
+    # set requested format and write all messages
+    chat.set_msg_format(args.format)
+    chat.msg_write(msgs)
 
 
 def hist_cmd(args: argparse.Namespace, config: Config) -> None: