diff --git a/bumble/device.py b/bumble/device.py
index f3b431c5..b39299cb 100644
--- a/bumble/device.py
+++ b/bumble/device.py
@@ -5442,7 +5442,7 @@ async def create_cs_config(
         role: int = hci.CsRole.INITIATOR,
         rtt_type: int = hci.RttType.AA_ONLY,
         cs_sync_phy: int = hci.CsSyncPhy.LE_1M,
-        channel_map: bytes = b'\x54\x55\x55\x54\x55\x55\x55\x55\x55\x15',
+        channel_map: bytes = b'\x54\x55\x55\x54\x55\x55\x55\x55\x55\x05',
         channel_map_repetition: int = 0x01,
         channel_selection_type: int = hci.HCI_LE_CS_Create_Config_Command.ChannelSelectionType.ALGO_3B,
         ch3c_shape: int = hci.HCI_LE_CS_Create_Config_Command.Ch3cShape.HAT,
diff --git a/tests/device_test.py b/tests/device_test.py
index 3efe4db1..c148fa4d 100644
--- a/tests/device_test.py
+++ b/tests/device_test.py
@@ -16,6 +16,7 @@
 # Imports
 # -----------------------------------------------------------------------------
 import asyncio
+import inspect
 import functools
 import logging
 import os
@@ -693,6 +694,25 @@ async def test_power_on_default_static_address_should_not_be_any():
     assert devices[0].static_address != Address.ANY_RANDOM
 
 
+# -----------------------------------------------------------------------------
+def test_cs_channel_map_excludes_forbidden_channels():
+    forbidden = {0, 1, 23, 24, 25, 76, 77, 78, 79}
+    default_map = inspect.signature(Device.create_cs_config).parameters[
+        'channel_map'
+    ].default
+
+    enabled = {
+        byte_idx * 8 + bit
+        for byte_idx, byte in enumerate(default_map)
+        for bit in range(8)
+        if byte & (1 << bit)
+    }
+
+    assert enabled.isdisjoint(forbidden), (
+        f"Default channel_map enables forbidden CS channels: {enabled & forbidden}"
+    )
+
+
 # -----------------------------------------------------------------------------
 def test_gatt_services_with_gas_and_gatt():
     device = Device(host=Host(None, None))