diff --git a/embed/bootloader/messages.c b/embed/bootloader/messages.c
index b1008a5ce3..d27bcc3f28 100644
--- a/embed/bootloader/messages.c
+++ b/embed/bootloader/messages.c
@@ -334,6 +334,7 @@ int process_msg_FirmwareUpload(uint8_t iface_num, uint32_t msg_size, uint8_t *bu
         return -1;
     }
 
+    uint32_t firstskip = 0;
     if (firmware_block == 0) {
         vendor_header vhdr;
         if (sectrue != load_vendor_header_keys(chunk_buffer, &vhdr)) {
@@ -350,6 +351,18 @@ int process_msg_FirmwareUpload(uint8_t iface_num, uint32_t msg_size, uint8_t *bu
             MSG_SEND(Failure);
             return -3;
         }
+
+        // TODO: erase storage if vendor is being changed
+
+        firstskip = IMAGE_HEADER_SIZE + vhdr.hdrlen;
+    }
+
+    if (sectrue != check_single_hash(hdr.hashes + firmware_block * 32, chunk_buffer + firstskip, chunk_size - firstskip)) {
+        MSG_SEND_INIT(Failure);
+        MSG_SEND_ASSIGN_VALUE(code, FailureType_Failure_ProcessError);
+        MSG_SEND_ASSIGN_STRING(message, "Invalid chunk hash");
+        MSG_SEND(Failure);
+        return -4;
     }
 
     if (sectrue != flash_unlock()) {
@@ -357,7 +370,7 @@ int process_msg_FirmwareUpload(uint8_t iface_num, uint32_t msg_size, uint8_t *bu
         MSG_SEND_ASSIGN_VALUE(code, FailureType_Failure_ProcessError);
         MSG_SEND_ASSIGN_STRING(message, "Could not unlock flash");
         MSG_SEND(Failure);
-        return -4;
+        return -5;
     }
 
     // TODO: fix writing to non-continous area
@@ -369,7 +382,7 @@ int process_msg_FirmwareUpload(uint8_t iface_num, uint32_t msg_size, uint8_t *bu
             MSG_SEND_ASSIGN_STRING(message, "Could not write data");
             MSG_SEND(Failure);
             flash_lock();
-            return -5;
+            return -6;
         }
     }
 
diff --git a/embed/trezorhal/image.c b/embed/trezorhal/image.c
index 74cee0480f..c20e0ebaa6 100644
--- a/embed/trezorhal/image.c
+++ b/embed/trezorhal/image.c
@@ -130,7 +130,7 @@ secbool load_vendor_header(const uint8_t * const data, uint8_t key_m, uint8_t ke
     return sectrue * (0 == ed25519_sign_open(hash, BLAKE2S_DIGEST_LENGTH, pub, *(const ed25519_signature *)vhdr->sig));
 }
 
-static secbool check_hash(const uint8_t * const hash, const uint8_t * const data, int len)
+secbool check_single_hash(const uint8_t * const hash, const uint8_t * const data, int len)
 {
     uint8_t h[BLAKE2S_DIGEST_LENGTH];
     blake2s(data, len, h, BLAKE2S_DIGEST_LENGTH);
@@ -146,7 +146,7 @@ secbool check_image_contents(const image_header * const hdr, uint32_t firstskip,
     }
     const void *data = (const void *)(FLASH_SECTOR_TABLE[sectors[0]] + firstskip);
     int remaining = hdr->codelen;
-    if (sectrue != check_hash(hdr->hashes, data, MIN(remaining, IMAGE_CHUNK_SIZE - firstskip))) {
+    if (sectrue != check_single_hash(hdr->hashes, data, MIN(remaining, IMAGE_CHUNK_SIZE - firstskip))) {
         return secfalse;
     }
     int block = 1;
@@ -156,7 +156,7 @@ secbool check_image_contents(const image_header * const hdr, uint32_t firstskip,
             return secfalse;
         }
         data = (const void *)FLASH_SECTOR_TABLE[sectors[block]];
-        if (sectrue != check_hash(hdr->hashes + block * 32, data, MIN(remaining, IMAGE_CHUNK_SIZE))) {
+        if (sectrue != check_single_hash(hdr->hashes + block * 32, data, MIN(remaining, IMAGE_CHUNK_SIZE))) {
             return secfalse;
         }
         block++;
diff --git a/embed/trezorhal/image.h b/embed/trezorhal/image.h
index 04570bbebb..87bc75bedc 100644
--- a/embed/trezorhal/image.h
+++ b/embed/trezorhal/image.h
@@ -13,10 +13,11 @@
 #define IMAGE_CHUNK_SIZE   (128 * 1024)
 
 #define BOOTLOADER_IMAGE_MAGIC   0x425A5254 // TRZB
-#define BOOTLOADER_IMAGE_MAXSIZE (1 * 128 * 1024)
+#define BOOTLOADER_IMAGE_MAXSIZE (1 * IMAGE_CHUNK_SIZE)
 
-#define FIRMWARE_IMAGE_MAGIC   0x465A5254 // TRZF
-#define FIRMWARE_IMAGE_MAXSIZE (6 * 128 * 1024)
+#define FIRMWARE_IMAGE_MAGIC     0x465A5254 // TRZF
+#define FIRMWARE_IMAGE_MAXSIZE   (6 * IMAGE_CHUNK_SIZE)
+// TODO: change above limitation to 13 blocks after fixing writing to non-continuous area
 
 typedef struct {
     uint32_t magic;
@@ -54,6 +55,8 @@ secbool load_image_header(const uint8_t * const data, const uint32_t magic, cons
 
 secbool load_vendor_header(const uint8_t * const data, uint8_t key_m, uint8_t key_n, const uint8_t * const *keys, vendor_header * const vhdr);
 
+secbool check_single_hash(const uint8_t * const hash, const uint8_t * const data, int len);
+
 secbool check_image_contents(const image_header * const hdr, uint32_t firstskip, const uint8_t *sectors, int blocks);
 
 #endif