diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 436f43f87da9..1e1ef210ae91 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -89,7 +89,7 @@ struct bio {
 	struct bio_vec		bi_inline_vecs[0];
 };
 
-#define BIO_OP_SHIFT	(8 * sizeof(unsigned int) - REQ_OP_BITS)
+#define BIO_OP_SHIFT	(8 * FIELD_SIZEOF(struct bio, bi_opf) - REQ_OP_BITS)
 #define bio_op(bio)	((bio)->bi_opf >> BIO_OP_SHIFT)
 
 #define bio_set_op_attrs(bio, op, op_flags) do {		\