diff --git a/bumble/hci.py b/bumble/hci.py
index a8403b9..9b5793d 100644
--- a/bumble/hci.py
+++ b/bumble/hci.py
@@ -2102,7 +2102,7 @@ class HCI_Link_Key_Request_Negative_Reply_Command(HCI_Command):
     fields=[
         ('bd_addr', Address.parse_address),
         ('pin_code_length', 1),
-        ('pin_code', '*'),
+        ('pin_code', 16),
     ],
     return_parameters_fields=[
         ('status', STATUS_SPEC),
diff --git a/tests/hci_test.py b/tests/hci_test.py
index 6529885..af68e86 100644
--- a/tests/hci_test.py
+++ b/tests/hci_test.py
@@ -215,12 +215,18 @@ def test_HCI_Command():
 
 # -----------------------------------------------------------------------------
 def test_HCI_PIN_Code_Request_Reply_Command():
+    pin_code = b'1234'
+    pin_code_length = len(pin_code)
+    # here to make the test pass, we need to
+    # pad pin_code, as HCI_Object.format_fields
+    # does not do it for us
+    padded_pin_code = pin_code + bytes(16 - pin_code_length)
     command = HCI_PIN_Code_Request_Reply_Command(
         bd_addr=Address(
             '00:11:22:33:44:55', address_type=Address.PUBLIC_DEVICE_ADDRESS
         ),
-        pin_code_length=4,
-        pin_code=b'1234',
+        pin_code_length=pin_code_length,
+        pin_code=padded_pin_code,
     )
     basic_check(command)