diff --git a/psptool/key_store_file.py b/psptool/key_store_file.py
index fe17c96..523a22e 100644
--- a/psptool/key_store_file.py
+++ b/psptool/key_store_file.py
@@ -81,9 +81,13 @@ def __init__(self, file):
 
         self.certifying_id = KeyId(self, 0x10, buffer_offset=0x38)
 
-        self._unknown_constant_1 = NestedBuffer(self, 0x4, buffer_offset=0x30)
-        self._unknown_constant_2 = NestedBuffer(self, 0x4, buffer_offset=0x34)
-        assert self.unknown_constants == (b'\1\0\0\0', b'\2\0\0\0')
+        # Same fields as in a HeaderFile. Early Renoir key stores leave the
+        # signature type at 0 next to a 0x200 byte signature, so
+        # signature_size is derived from the sizes instead.
+        self._signed = NestedBuffer(self, 0x4, buffer_offset=0x30)
+        self._signature_type = NestedBuffer(self, 0x4, buffer_offset=0x34)
+        assert self.signed == 1
+        assert self.signature_type in {0, 2}
 
         self._keystore_type = NestedBuffer(self, 0x4, buffer_offset=0x7c)
         assert self.keystore_type in File.KEY_STORE_TYPES or self.keystore_type == 0
@@ -130,11 +134,12 @@ def signature_size(self) -> int:
             return self.parent_buffer.buffer_size - self.body_size - self.HEADER_SIZE
 
     @property
-    def unknown_constants(self) -> (bytes, bytes, bytes):
-        return (
-                self._unknown_constant_1.get_bytes(),
-                self._unknown_constant_2.get_bytes(),
-                )
+    def signed(self) -> int:
+        return int.from_bytes(self._signed.get_bytes(), 'little')
+
+    @property
+    def signature_type(self) -> int:
+        return int.from_bytes(self._signature_type.get_bytes(), 'little')
 
 
 class KeyStore(NestedBuffer):
diff --git a/tests/unit/test_key_store_file.py b/tests/unit/test_key_store_file.py
new file mode 100644
index 0000000..875c90b
--- /dev/null
+++ b/tests/unit/test_key_store_file.py
@@ -0,0 +1,91 @@
+# PSPTool - Display, extract and manipulate PSP firmware inside UEFI images
+# Copyright (C) 2026 contributors
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+"""Synthetic ROMs holding a single 0x50 key store.
+
+Key stores in early ThinkPad T14/X13 Gen 1 AMD releases have no $PS1
+magic and signature type 0 next to a 0x200 byte signature.
+"""
+
+import contextlib
+import io
+import os
+import struct
+import tempfile
+import unittest
+
+from psptool import PSPTool
+from psptool.blob import Blob
+from psptool.utils import fletcher32
+
+ROM_SIZE = 8 * 1024 * 1024
+FET_OFFSET = Blob.POSSIBLE_FET_OFFSETS[0]
+PSP_DIR_OFFSET = FET_OFFSET + 0x1000
+KEY_STORE_OFFSET = FET_OFFSET + 0x2000
+HEADER_FILE_SIZE = 0x100
+
+# Directory additional_info: version bit set, address mode 1 (flash offset)
+FLASH_OFFSET_MODE = (1 << 31) | (1 << 24)
+
+
+def key_store_file(magic: bytes, signature_type: int) -> bytes:
+    modulus_size = 0x100
+    key = struct.pack('<IIII', 0x50 + modulus_size, 1, 0, 0x10001)
+    key += bytes(0x10) + struct.pack('<I', modulus_size * 8)
+    key = key.ljust(0x50, b'\0') + bytes(modulus_size)
+    key_store = struct.pack('<II', 0x50 + len(key), 1) + b'$KDB'
+    key_store = key_store.ljust(0x50, b'\0') + key
+    signature_size = 0x200
+    header = bytearray(HEADER_FILE_SIZE)
+    header[0x10:0x14] = magic
+    header[0x14:0x18] = struct.pack('<I', len(key_store))
+    header[0x30:0x38] = struct.pack('<II', 1, signature_type)
+    header[0x6c:0x70] = struct.pack('<I', HEADER_FILE_SIZE + len(key_store) + signature_size)
+    header[0x7c:0x80] = struct.pack('<I', 0x50)
+    return bytes(header) + key_store + bytes(signature_size)
+
+
+def rom(ksf: bytes) -> bytes:
+    blob = bytearray(ROM_SIZE)
+    blob[FET_OFFSET - 4:FET_OFFSET] = b'\xff' * 4
+    blob[FET_OFFSET:FET_OFFSET + 4] = Blob._FIRMWARE_ENTRY_MAGIC
+    blob[FET_OFFSET + 4:FET_OFFSET + 8] = struct.pack('<I', PSP_DIR_OFFSET)
+    blob[FET_OFFSET + 8:FET_OFFSET + 24] = b'\xff' * 16
+    body = struct.pack('<II', 1, FLASH_OFFSET_MODE)
+    body += struct.pack('<BBHIII', 0x50, 0, 0, len(ksf), KEY_STORE_OFFSET, 0)
+    psp_dir = b'$PSP' + fletcher32(body) + body
+    blob[PSP_DIR_OFFSET:PSP_DIR_OFFSET + len(psp_dir)] = psp_dir
+    blob[KEY_STORE_OFFSET:KEY_STORE_OFFSET + len(ksf)] = ksf
+    return bytes(blob)
+
+
+def parse(data: bytes):
+    with tempfile.NamedTemporaryFile(suffix='.rom', delete=False) as f:
+        f.write(data)
+        path = f.name
+    try:
+        with io.StringIO() as stderr, contextlib.redirect_stderr(stderr):
+            return PSPTool.from_file(path)
+    finally:
+        os.unlink(path)
+
+
+class TestKeyStoreFile(unittest.TestCase):
+
+    def test_key_store_with_signature_type_0(self):
+        for magic, signature_type in ((b'$PS1', 2), (bytes(4), 0)):
+            with self.subTest(magic=magic, signature_type=signature_type):
+                pt = parse(rom(key_store_file(magic, signature_type)))
+                (key_store,) = pt.blob.unique_files()
+                self.assertEqual(type(key_store).__name__, 'KeyStoreFile')
+                self.assertEqual(key_store.signature.buffer_size, 0x200)
+                self.assertEqual(len(key_store.key_store.keys), 1)
+
+
+if __name__ == '__main__':
+    unittest.main()