diff --git a/src/usb/uf2/ghostfat.c b/src/usb/uf2/ghostfat.c
index 6bd5a86..bb68303 100644
--- a/src/usb/uf2/ghostfat.c
+++ b/src/usb/uf2/ghostfat.c
@@ -248,7 +248,7 @@ void read_block(uint32_t block_no, uint8_t *data) {
         } else {
             sectionIdx -= NUM_INFO - 1;
             uint32_t addr = USER_FLASH_START + sectionIdx * 256;
-            if (addr < FLASH_SIZE) {
+            if (addr < USER_FLASH_START+FLASH_SIZE) {
                 UF2_Block *bl = (void *)data;
                 bl->magicStart0 = UF2_MAGIC_START0;
                 bl->magicStart1 = UF2_MAGIC_START1;
diff --git a/src/usb/uf2/uf2cfg.h b/src/usb/uf2/uf2cfg.h
index e3ea9b1..18efd58 100644
--- a/src/usb/uf2/uf2cfg.h
+++ b/src/usb/uf2/uf2cfg.h
@@ -6,10 +6,10 @@
 
 #define UF2_NUM_BLOCKS 8000   // at least 4,1 MB for FAT16
 #define VOLUME_LABEL "NRF52BOOT  "
-#define FLASH_SIZE (BOOTLOADER_REGION_START-USER_FLASH_START)
+#define FLASH_SIZE (10*1024) //(USER_FLASH_END-USER_FLASH_START)
 
 // Only allow to write application
 #define USER_FLASH_START 0x26000
-#define USER_FLASH_END BOOTLOADER_REGION_START
+#define USER_FLASH_END   0xAD000 // Fat Fs start here
 
 #define FLASH_PAGE_SIZE 4096