diff --git a/bot.py b/bot.py
index ca198ea..aa65f6e 100755
--- a/bot.py
+++ b/bot.py
@@ -75,12 +75,12 @@ class BotClient(discord.Client):
         command = message.content.split(" ")[0]
         match command:
             case "%calc":
-                reply = await _calculate(command[1:])
+                reply = await self._calculate(command[1:])
                 await message.reply(content=reply)
             case _:
                 _log.info(f"Unrecognised command {command}")
 
-    async def _calculate(args: list[str]) -> str:
+    async def _calculate(self, args: list[str]) -> str:
         proc = sp.run(["node", "calc_main.js", "--"] + args)
         msg = proc.stdout
         return msg.strip()