diff --git a/aiogram/types/inline_keyboard.py b/aiogram/types/inline_keyboard.py
index 7c859e6e..56094709 100644
--- a/aiogram/types/inline_keyboard.py
+++ b/aiogram/types/inline_keyboard.py
@@ -64,7 +64,7 @@ class InlineKeyboardMarkup(base.TelegramObject):
 
         :param button:
         """
-        if self.inline_keyboard and len(self.inline_keyboard[-1] < self.row_width):
+        if self.inline_keyboard and len(self.inline_keyboard[-1]) < self.row_width:
             self.inline_keyboard[-1].append(button)
         else:
             self.add(button)