diff --git a/src/usb/uf2/ghostfat.c b/src/usb/uf2/ghostfat.c
index de49f38..ce8c297 100644
--- a/src/usb/uf2/ghostfat.c
+++ b/src/usb/uf2/ghostfat.c
@@ -297,6 +297,11 @@ int write_block(uint32_t block_no, uint8_t *data, bool quiet/*, WriteState *stat
         return -1;
     }
 
+    // only accept block with same family id
+    if ( UF2_FAMILY_ID && !((bl->flags & UF2_FLAG_FAMILYID) && (bl->familyID == UF2_FAMILY_ID)) ) {
+      return -1;
+    }
+
     if ((bl->flags & UF2_FLAG_NOFLASH) || bl->payloadSize > 256 || (bl->targetAddr & 0xff) ||
         bl->targetAddr < USER_FLASH_START || bl->targetAddr + bl->payloadSize > USER_FLASH_END) {
 #if USE_DBG_MSC
diff --git a/src/usb/uf2/uf2.h b/src/usb/uf2/uf2.h
index f909c24..6edbb4f 100644
--- a/src/usb/uf2/uf2.h
+++ b/src/usb/uf2/uf2.h
@@ -51,6 +51,7 @@ extern bool sdRunning;
 
 // If set, the block is "comment" and should not be flashed to the device
 #define UF2_FLAG_NOFLASH 0x00000001
+#define UF2_FLAG_FAMILYID 0x00002000
 
 #define MAX_BLOCKS (FLASH_SIZE / 256 + 100)
 typedef struct {
@@ -68,7 +69,7 @@ typedef struct {
     uint32_t payloadSize;
     uint32_t blockNo;
     uint32_t numBlocks;
-    uint32_t reserved;
+    uint32_t familyID;
 
     // raw data;
     uint8_t data[476];
diff --git a/src/usb/uf2/uf2cfg.h b/src/usb/uf2/uf2cfg.h
index 815efe2..fe8f08e 100644
--- a/src/usb/uf2/uf2cfg.h
+++ b/src/usb/uf2/uf2cfg.h
@@ -13,3 +13,5 @@
 #define USER_FLASH_END     0xAD000 // Fat Fs start here
 
 #define FLASH_PAGE_SIZE    4096
+
+#define UF2_FAMILY_ID      0xADA52840