diff --git a/fs/bcachefs/extents.c b/fs/bcachefs/extents.c
index 76b2459d8e73..2be49f443eb0 100644
--- a/fs/bcachefs/extents.c
+++ b/fs/bcachefs/extents.c
@@ -1183,7 +1183,7 @@ int bch2_cut_back_s(struct bpos where, struct bkey_s k)
 
 	len = where.offset - bkey_start_offset(k.k);
 
-	k.k->p = where;
+	k.k->p.offset = where.offset;
 	k.k->size = len;
 
 	if (!len) {