diff --git a/megacom/__init__.py b/megacom/__init__.py
index 8cc3926..8663f0a 100644
--- a/megacom/__init__.py
+++ b/megacom/__init__.py
@@ -104,7 +104,8 @@ async def megacom(tty: str, baud: int, mode: str) -> None:
 
     m = MODE_RE.match(mode)
     if m is None:
-        raise Exception(f"invalid mode: {mode}")
+        sys.stderr.write(f"invalid mode: {mode}\n")
+        sys.exit(1)
     bytesize = MODE_LOOKUP["bytesize"][m.group(1)]
     parity = MODE_LOOKUP["parity"][m.group(2)]
     stopbits = MODE_LOOKUP["stopbits"][m.group(3)]