diff --git a/export-image/prerun.sh b/export-image/prerun.sh
index 8104f45..cec133c 100755
--- a/export-image/prerun.sh
+++ b/export-image/prerun.sh
@@ -12,7 +12,8 @@ mkdir -p ${ROOTFS_DIR}
 BOOT_SIZE=$(du --apparent-size -s ${EXPORT_ROOTFS_DIR}/boot --block-size=1 | cut -f 1)
 TOTAL_SIZE=$(du --apparent-size -s ${EXPORT_ROOTFS_DIR} --exclude var/cache/apt/archives --block-size=1 | cut -f 1)
 
-IMG_SIZE=$((BOOT_SIZE + TOTAL_SIZE + (800 * 1024 * 1024)))
+ROUND_SIZE="$((4 * 1024 * 1024))"
+IMG_SIZE=$(((BOOT_SIZE + TOTAL_SIZE + (800 * 1024 * 1024) + ROUND_SIZE) / ROUND_SIZE * ROUND_SIZE))
 
 truncate -s ${IMG_SIZE} ${IMG_FILE}
 fdisk -H 255 -S 63 ${IMG_FILE} <<EOF