diff --git a/block-vvfat.c b/block-vvfat.c
index 429c37c5e7..79059311c6 100644
--- a/block-vvfat.c
+++ b/block-vvfat.c
@@ -509,9 +509,12 @@ static inline uint8_t fat_chksum(const direntry_t* entry)
     uint8_t chksum=0;
     int i;
 
-    for(i=0;i<11;i++)
-	chksum=(((chksum&0xfe)>>1)|((chksum&0x01)?0x80:0))
-	    +(unsigned char)entry->name[i];
+    for(i=0;i<11;i++) {
+        unsigned char c;
+
+        c = (i <= 8) ? entry->name[i] : entry->extension[i-8];
+        chksum=(((chksum&0xfe)>>1)|((chksum&0x01)?0x80:0)) + c;
+    }
 
     return chksum;
 }