diff --git a/bot.py b/bot.py
index b609cd0..0ae9000 100755
--- a/bot.py
+++ b/bot.py
@@ -81,7 +81,9 @@ class BotClient(discord.Client):
 
     async def _calculate(self, args: list[str]) -> str:
         proc = sp.run(["node", "calc_main.js", "--"] + args)
-        msg = proc.stdout
+        if proc.returncode != 0:
+            _log.error(f"running calculator: {proc.stderr}")
+        msg = proc.stdout or ""
         return msg.strip()
 
     def is_replay(self, message: discord.Message) -> bool: