diff --git a/docs/memory.md b/docs/memory.md
index b05d3056..35d7db90 100644
--- a/docs/memory.md
+++ b/docs/memory.md
@@ -35,7 +35,7 @@
 |----------|-------------------------|------|--------------------------------
 | block  0 | 0x1FFF7800 - 0x1FFF781F | 32 B | device manufacturing date
 | block  1 | 0x1FFF7820 - 0x1FFF783F | 32 B | bootloader downgrade protection
-| block  2 | 0x1FFF7840 - 0x1FFF785F | 32 B | unused
+| block  2 | 0x1FFF7840 - 0x1FFF785F | 32 B | vendor keys lock
 | block  3 | 0x1FFF7860 - 0x1FFF787F | 32 B | unused
 | block  4 | 0x1FFF7880 - 0x1FFF789F | 32 B | unused
 | block  5 | 0x1FFF78A0 - 0x1FFF78BF | 32 B | unused
diff --git a/embed/bootloader/main.c b/embed/bootloader/main.c
index b14add34..cec56702 100644
--- a/embed/bootloader/main.c
+++ b/embed/bootloader/main.c
@@ -259,7 +259,7 @@ secbool bootloader_loop(secbool firmware_present)
 
 // protection against bootloader downgrade
 
-#define BOOTLOADER_VERSION_OTP_BLOCK 1
+#define OTP_BLOCK_BOOTLOADER_VERSION 1
 
 void check_bootloader_version(void)
 {
@@ -271,10 +271,10 @@ void check_bootloader_version(void)
              bits[i / 8] |= (1 << (7 - (i % 8)));
         }
     }
-    ensure(flash_otp_write(BOOTLOADER_VERSION_OTP_BLOCK, 0, bits, FLASH_OTP_BLOCK_SIZE), NULL);
+    ensure(flash_otp_write(OTP_BLOCK_BOOTLOADER_VERSION, 0, bits, FLASH_OTP_BLOCK_SIZE), NULL);
 
     uint8_t bits2[FLASH_OTP_BLOCK_SIZE];
-    ensure(flash_otp_read(BOOTLOADER_VERSION_OTP_BLOCK, 0, bits2, FLASH_OTP_BLOCK_SIZE), NULL);
+    ensure(flash_otp_read(OTP_BLOCK_BOOTLOADER_VERSION, 0, bits2, FLASH_OTP_BLOCK_SIZE), NULL);
 
     ensure(sectrue * (0 == memcmp(bits, bits2, FLASH_OTP_BLOCK_SIZE)), "Bootloader downgraded");
 }
@@ -284,6 +284,19 @@ secbool load_vendor_header_keys(const uint8_t * const data, vendor_header * cons
     return load_vendor_header(data, BOOTLOADER_KEY_M, BOOTLOADER_KEY_N, BOOTLOADER_KEYS, vhdr);
 }
 
+#define OTP_BLOCK_VENDOR_KEYS_LOCK 2
+
+secbool check_vendor_keys_lock(const vendor_header * const vhdr) {
+    uint8_t lock[FLASH_OTP_BLOCK_SIZE];
+    ensure(flash_otp_read(OTP_BLOCK_VENDOR_KEYS_LOCK, 0, lock, FLASH_OTP_BLOCK_SIZE), NULL);
+    if (0 == memcmp(lock, "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF", FLASH_OTP_BLOCK_SIZE)) {
+        return sectrue;
+    }
+    uint8_t hash[32];
+    vendor_keys_hash(vhdr, hash);
+    return sectrue * (0 == memcmp(lock, hash, 32));
+}
+
 int main(void)
 {
 #if PRODUCTION
@@ -316,6 +329,10 @@ int main(void)
         load_vendor_header_keys((const uint8_t *)FIRMWARE_START, &vhdr),
         "invalid vendor header");
 
+    ensure(
+        check_vendor_keys_lock(&vhdr),
+        "unauthorized vendor keys");
+
     image_header hdr;
 
     ensure(