diff --git a/embed/prodtest/main.c b/embed/prodtest/main.c
index 12459996bd..448e64b880 100644
--- a/embed/prodtest/main.c
+++ b/embed/prodtest/main.c
@@ -352,7 +352,7 @@ static void test_otp_write(const char *args)
     memzero(data, sizeof(data));
     strncpy(data, args, sizeof(data) - 1);
     ensure(flash_otp_write(FLASH_OTP_BLOCK_BATCH, 0, (const uint8_t *) data, sizeof(data)), NULL);
-    ensure(flash_otp_lock(0), NULL);
+    ensure(flash_otp_lock(FLASH_OTP_BLOCK_BATCH), NULL);
     vcp_printf("OK");
 }
 
diff --git a/embed/trezorhal/common.c b/embed/trezorhal/common.c
index 07c4776bec..c3afd92619 100644
--- a/embed/trezorhal/common.c
+++ b/embed/trezorhal/common.c
@@ -151,6 +151,7 @@ void collect_hw_entropy(void)
         uint8_t entropy[FLASH_OTP_BLOCK_SIZE];
         random_buffer(entropy, FLASH_OTP_BLOCK_SIZE);
         ensure(flash_otp_write(FLASH_OTP_BLOCK_RANDOMNESS, 0, entropy, FLASH_OTP_BLOCK_SIZE), NULL);
+        ensure(flash_otp_lock(FLASH_OTP_BLOCK_RANDOMNESS), NULL);
     }
     // collect entropy from OTP randomness block
     ensure(flash_otp_read(FLASH_OTP_BLOCK_RANDOMNESS, 0, HW_ENTROPY_DATA + 12, FLASH_OTP_BLOCK_SIZE), NULL);