diff --git a/services/telegram_bot_service.py b/services/telegram_bot_service.py
index 6cb5927..c453555 100644
--- a/services/telegram_bot_service.py
+++ b/services/telegram_bot_service.py
@@ -164,7 +164,7 @@ class TrendTelegramBot:
         ]
         return InlineKeyboardMarkup(keyboard)
 
-    def _get_category_keyboard(self, callback_prefix: str = "cat"):
+    def _get_category_keyboard(self, callback_prefix: str = "trend"):
         """建立分類選擇按鈕"""
         # 每行 3 個按鈕
         keyboard = []
diff --git a/tests/test_trend_telegram_bot_service.py b/tests/test_trend_telegram_bot_service.py
index 02c5a24..11fe8dc 100644
--- a/tests/test_trend_telegram_bot_service.py
+++ b/tests/test_trend_telegram_bot_service.py
@@ -50,6 +50,21 @@ def _run(coro):
     return asyncio.run(coro)
 
 
+def test_default_category_keyboard_uses_handled_trend_prefix():
+    from services.telegram_bot_service import CATEGORIES, TrendTelegramBot
+
+    bot = TrendTelegramBot(token="dummy")
+    keyboard = bot._get_category_keyboard()
+    callback_values = [
+        button.callback_data
+        for row in keyboard.inline_keyboard
+        for button in row
+    ]
+
+    assert f"trend_{CATEGORIES[0]}" in callback_values
+    assert not any(value.startswith("cat_") for value in callback_values)
+
+
 def test_polling_callback_dedup_without_update_id(monkeypatch):
     from services.telegram_bot_service import TrendTelegramBot