diff --git a/adafruit_ble/services/apple.py b/adafruit_ble/services/apple.py
index cfa1bb1..115192e 100755
--- a/adafruit_ble/services/apple.py
+++ b/adafruit_ble/services/apple.py
@@ -165,6 +165,8 @@ def __str__(self):
         category = None
         if self.category_id < len(NOTIFICATION_CATEGORIES):
             category = NOTIFICATION_CATEGORIES[self.category_id]
+        else:
+            category = "Reserved"
 
         if self.silent:
             flags.append("silent")