diff --git a/slot_change_finder.py b/slot_change_finder.py
index f7ba47b..d0c6db2 100644
--- a/slot_change_finder.py
+++ b/slot_change_finder.py
@@ -13,7 +13,8 @@ def parse_slot(s: str) -> int:
 
 def checksum(addr: str) -> str:
     if not Web3.is_address(addr):
-        print("❌ Invalid Ethereum address."); sys.exit(2)
+        print("❌ Invalid Ethereum address.", file=sys.stderr)
+        sys.exit(2)
     return Web3.to_checksum_address(addr)
 
 def connect(url: str) -> Web3: