diff --git a/bot.py b/bot.py
index 82d0c1e..4a0e713 100755
--- a/bot.py
+++ b/bot.py
@@ -101,8 +101,11 @@ class BotClient(discord.Client):
         proc = sp.run(
             ["node", "calc_main.js", "--"] + args, stdout=sp.PIPE, stderr=sp.PIPE
         )
+        stderr = proc.stderr.decode()
         if proc.returncode != 0:
             raise Exception(proc.stderr.decode())
+        if stderr:
+            _log.warning(f"running calculation '{args}': {stderr}")
         return proc.stdout.decode()
 
     def is_replay(self, message: discord.Message) -> bool: