--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@@ -356,7 +356,14 @@ static int part_unlock(struct mtd_info *
 	struct mtd_part *part = PART(mtd);
 	if ((len + ofs) > mtd->size)
 		return -EINVAL;
-	return mtd_unlock(part->master, ofs + part->offset, len);
+
+	ofs += part->offset;
+	if (mtd->flags & MTD_ERASE_PARTIAL) {
+		/* round up len to next erasesize and round down offset to prev block */
+		len = (mtd_div_by_eb(len, part->master) + 1) * part->master->erasesize;
+		ofs &= ~(part->master->erasesize - 1);
+	}
+	return mtd_unlock(part->master, ofs, len);
 }
 
 static int part_is_locked(struct mtd_info *mtd, loff_t ofs, uint64_t len)