diff --git a/telegram_bot/bot.py b/telegram_bot/bot.py
index 83667ba..fabe6ec 100644
--- a/telegram_bot/bot.py
+++ b/telegram_bot/bot.py
@@ -468,13 +468,13 @@ def set_new_transaction(message):
     :rtype: none
     """
     user_id = int(message.from_user.id)
-    bot.send_message(chat_id=user_id, text='Type "<name of stock>,<isin>,<amount>,<price_per_stock_usd>" (time of transaction will be set to now):')
+    bot.send_message(chat_id=user_id, text='Type "<name of stock>,<isin>,<amount>,<price_per_stock_usd>" (time of transaction will be set to now, negative amount is selling, positive is buying):')
     bot.register_next_step_handler(message, set_new_transaction_step)
 
 def set_new_transaction_step(message):
     user_id = int(message.from_user.id)
 
-    if not re.match(r"[A-Za-z0-9]+,[A-Za-z0-9]+,[0-9]+(.[0-9]+)?,[0-9]+(.[0-9]+)?", message.text):
+    if not re.match(r"[A-Za-z0-9]+,[A-Za-z0-9]+,(-)?[0-9]+(.[0-9]+)?,[0-9]+(.[0-9]+)?", message.text):
         bot.send_message(chat_id=user_id, text='Invalid format \n(e.g. Apple,US0378331005,53.2,120.4).\n Try again with /newtransaction.')
         return