diff --git a/radio/src/io/bootloader_flash.cpp b/radio/src/io/bootloader_flash.cpp
index 20a7947de..09b3fc81b 100644
--- a/radio/src/io/bootloader_flash.cpp
+++ b/radio/src/io/bootloader_flash.cpp
@@ -59,8 +59,11 @@ void BootloaderFirmwareUpdate::flashFirmware(const char * filename, ProgressHand
   }
 
   for (int i = 0; i < BOOTLOADER_SIZE; i += 1024) {
+
     watchdogSuspend(1000/*10s*/);
-    if (f_read(&file, buffer, sizeof(buffer), &count) != FR_OK || count != sizeof(buffer)) {
+    memset(buffer, 0xFF, sizeof(buffer));
+
+    if (f_read(&file, buffer, sizeof(buffer), &count) != FR_OK) {
       POPUP_WARNING(STR_SDCARD_ERROR);
       break;
     }
@@ -68,12 +71,18 @@ void BootloaderFirmwareUpdate::flashFirmware(const char * filename, ProgressHand
       POPUP_WARNING(STR_INCOMPATIBLE);
       break;
     }
-    for (int j = 0; j < 1024; j += FLASH_PAGESIZE) {
+    for (UINT j = 0; j < count; j += FLASH_PAGESIZE) {
       flashWrite(CONVERT_UINT_PTR(FIRMWARE_ADDRESS + i + j), CONVERT_UINT_PTR(buffer + j));
     }
 
+    // TODO: use real bootloader size rather than the maximum size
     progressHandler("Bootloader", STR_WRITING, i, BOOTLOADER_SIZE);
 
+    // Reached end-of-file
+    if (count != sizeof(buffer)) {
+      break;
+    }
+
 #if defined(SIMU)
     // add an artificial delay and check for simu quit
     if (SIMU_SLEEP_OR_EXIT_MS(30))