diff --git a/aiogram/types/inline_keyboard.py b/aiogram/types/inline_keyboard.py
index 1b5c8011..69049345 100644
--- a/aiogram/types/inline_keyboard.py
+++ b/aiogram/types/inline_keyboard.py
@@ -69,7 +69,7 @@ class InlineKeyboardMarkup(base.TelegramObject):
         :return: self
         :rtype: :obj:`types.InlineKeyboardMarkup`
         """
-        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)