diff --git a/embed/boardloader/main.c b/embed/boardloader/main.c
index 8cab160e8..dc9a512f1 100644
--- a/embed/boardloader/main.c
+++ b/embed/boardloader/main.c
@@ -144,6 +144,10 @@ int main(void)
 {
     __stack_chk_guard = rng_get();
 
+#if PRODUCTION
+    flash_set_option_bytes();
+#endif
+
     clear_otg_hs_memory();
     periph_init();
 
diff --git a/embed/bootloader/main.c b/embed/bootloader/main.c
index 7643dcc87..e76787a0e 100644
--- a/embed/bootloader/main.c
+++ b/embed/bootloader/main.c
@@ -176,10 +176,36 @@ void mainloop(void)
     }
 }
 
+// protection against bootloader downgrade
+
+#define BOOTLOADER_VERSION_OTP_BLOCK 1
+
+void check_bootloader_version(void)
+{
+    uint8_t bits[FLASH_OTP_BLOCK_SIZE];
+    for (int i = 0; i < FLASH_OTP_BLOCK_SIZE * 8; i++) {
+        if (i < VERSION_MONOTONIC) {
+             bits[i / 8] &= ~(1 << (7 - (i % 8)));
+        } else {
+             bits[i / 8] |= (1 << (7 - (i % 8)));
+        }
+    }
+    trassert(true == flash_otp_write(BOOTLOADER_VERSION_OTP_BLOCK, 0, bits, FLASH_OTP_BLOCK_SIZE), NULL);
+
+    uint8_t bits2[FLASH_OTP_BLOCK_SIZE];
+    trassert(true == flash_otp_read(BOOTLOADER_VERSION_OTP_BLOCK, 0, bits2, FLASH_OTP_BLOCK_SIZE), NULL);
+
+    trassert(0 == memcmp(bits, bits2, FLASH_OTP_BLOCK_SIZE), "Bootloader downgraded");
+}
+
 int main(void)
 {
     __stack_chk_guard = rng_get();
 
+#if PRODUCTION
+    check_bootloader_version();
+#endif
+
     periph_init();
 
     display_pwm_init();
diff --git a/embed/bootloader/version.h b/embed/bootloader/version.h
index a62341fe9..c30364ead 100644
--- a/embed/bootloader/version.h
+++ b/embed/bootloader/version.h
@@ -2,3 +2,5 @@
 #define VERSION_MINOR 1
 #define VERSION_PATCH 0
 #define VERSION_BUILD 0
+
+#define VERSION_MONOTONIC 1
diff --git a/embed/trezorhal/flash.c b/embed/trezorhal/flash.c
index ea9560b3b..ad1b180aa 100644
--- a/embed/trezorhal/flash.c
+++ b/embed/trezorhal/flash.c
@@ -56,8 +56,6 @@ bool flash_write_word(uint32_t address, uint32_t data)
 }
 
 #define FLASH_OTP_LOCK_BASE       0x1FFF7A00U
-#define FLASH_OTP_NUM_BLOCKS      16
-#define FLASH_OTP_BLOCK_SIZE      32
 
 bool flash_otp_read(uint8_t block, uint8_t offset, uint8_t *data, uint8_t datalen)
 {
diff --git a/embed/trezorhal/flash.h b/embed/trezorhal/flash.h
index 085368cc8..94ffb898d 100644
--- a/embed/trezorhal/flash.h
+++ b/embed/trezorhal/flash.h
@@ -24,6 +24,9 @@ bool flash_erase_sectors(int start, int end, void (*progress)(uint16_t val));
 bool flash_write_byte(uint32_t address, uint8_t data);
 bool flash_write_word(uint32_t address, uint32_t data);
 
+#define FLASH_OTP_NUM_BLOCKS      16
+#define FLASH_OTP_BLOCK_SIZE      32
+
 bool flash_otp_read(uint8_t block, uint8_t offset, uint8_t *data, uint8_t datalen);
 bool flash_otp_write(uint8_t block, uint8_t offset, const uint8_t *data, uint8_t datalen);
 bool flash_otp_lock(uint8_t block);