diff --git a/sbin/fsck_msdosfs/boot.c b/sbin/fsck_msdosfs/boot.c
index 319518349eb3..b1760c5c02df 100644
--- a/sbin/fsck_msdosfs/boot.c
+++ b/sbin/fsck_msdosfs/boot.c
@@ -181,7 +181,7 @@ readboot(int dosfs, struct bootblock *boot)
 	    boot->bpbResSectors + boot->bpbFATs * boot->FATsecs -
 	    CLUST_FIRST * boot->bpbSecPerClust;
 
-	if (boot->bpbBytesPerSec % DOSBOOTBLOCKSIZE != 0) {
+	if (boot->bpbBytesPerSec % DOSBOOTBLOCKSIZE_REAL != 0) {
 		pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
 		return FSFATAL;
 	}
diff --git a/sbin/fsck_msdosfs/dosfs.h b/sbin/fsck_msdosfs/dosfs.h
index bd01b2423119..485b3a15e668 100644
--- a/sbin/fsck_msdosfs/dosfs.h
+++ b/sbin/fsck_msdosfs/dosfs.h
@@ -30,7 +30,9 @@
 #ifndef DOSFS_H
 #define DOSFS_H
 
-#define DOSBOOTBLOCKSIZE 512
+/* support 4Kn disk reads */
+#define DOSBOOTBLOCKSIZE_REAL 512
+#define DOSBOOTBLOCKSIZE 4096
 
 typedef	u_int32_t	cl_t;	/* type holding a cluster number */
 
diff --git a/sys/boot/amd64/boot1.efi/boot1.c b/sys/boot/amd64/boot1.efi/boot1.c
index eb27846383ab..cb75d2a12f47 100644
--- a/sys/boot/amd64/boot1.efi/boot1.c
+++ b/sys/boot/amd64/boot1.efi/boot1.c
@@ -168,9 +168,12 @@ static int
 dskread(void *buf, u_int64_t lba, int nblk)
 {
 	EFI_STATUS status;
+	int size;
 
+	lba = lba / (bootdev->Media->BlockSize / DEV_BSIZE);
+	size = nblk * DEV_BSIZE;
 	status = bootdev->ReadBlocks(bootdev, bootdev->Media->MediaId, lba,
-	    nblk * bootdev->Media->BlockSize, buf);
+	    size, buf);
 
 	if (EFI_ERROR(status))
 		return (-1);