diff --git a/legacy/emulator/memory.c b/legacy/emulator/memory.c
index 3cca42c68..b4bca60a5 100644
--- a/legacy/emulator/memory.c
+++ b/legacy/emulator/memory.c
@@ -122,7 +122,7 @@ void svc_flash_program(uint32_t size) {
   (void)size;
   assert(!flash_locked);
 }
-void svc_flash_erase_sector(uint16_t sector) {
+void svc_flash_erase_sector(uint8_t sector) {
   assert(!flash_locked);
   assert(sector >= FLASH_STORAGE_SECTOR_FIRST &&
          sector <= FLASH_STORAGE_SECTOR_LAST);
diff --git a/legacy/supervise.c b/legacy/supervise.c
index 85f07b7b7..2a41cb81c 100644
--- a/legacy/supervise.c
+++ b/legacy/supervise.c
@@ -45,7 +45,7 @@ static void svhandler_flash_program(uint32_t psize) {
   FLASH_CR |= FLASH_CR_PG;
 }
 
-static void svhandler_flash_erase_sector(uint16_t sector) {
+static void svhandler_flash_erase_sector(uint8_t sector) {
   /* we only allow erasing storage sectors 2 and 3. */
   if (sector < FLASH_STORAGE_SECTOR_FIRST ||
       sector > FLASH_STORAGE_SECTOR_LAST) {
diff --git a/legacy/supervise.h b/legacy/supervise.h
index c466cad31..7da11190b 100644
--- a/legacy/supervise.h
+++ b/legacy/supervise.h
@@ -87,7 +87,7 @@ inline void svc_reboot_to_bootloader(void) {
 
 extern void svc_flash_unlock(void);
 extern void svc_flash_program(uint32_t program_size);
-extern void svc_flash_erase_sector(uint16_t sector);
+extern void svc_flash_erase_sector(uint8_t sector);
 extern uint32_t svc_flash_lock(void);
 extern uint32_t svc_timer_ms(void);