diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 8692ab3fe6..44f44fcb1a 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1756,7 +1756,7 @@ static void check_object(struct object_entry *entry)
 				entry->delta_sibling_idx = base_entry->delta_child_idx;
 				SET_DELTA_CHILD(base_entry, entry);
 			} else {
-				SET_DELTA_EXT(entry, base_ref.hash);
+				SET_DELTA_EXT(entry, &base_ref);
 			}
 
 			unuse_pack(&w_curs);
diff --git a/pack-objects.c b/pack-objects.c
index 5e5a3c62d9..f2a433885a 100644
--- a/pack-objects.c
+++ b/pack-objects.c
@@ -203,14 +203,14 @@ struct object_entry *packlist_alloc(struct packing_data *pdata,
 
 void oe_set_delta_ext(struct packing_data *pdata,
 		      struct object_entry *delta,
-		      const unsigned char *sha1)
+		      const struct object_id *oid)
 {
 	struct object_entry *base;
 
 	ALLOC_GROW(pdata->ext_bases, pdata->nr_ext + 1, pdata->alloc_ext);
 	base = &pdata->ext_bases[pdata->nr_ext++];
 	memset(base, 0, sizeof(*base));
-	hashcpy(base->idx.oid.hash, sha1);
+	oidcpy(&base->idx.oid, oid);
 
 	/* These flags mark that we are not part of the actual pack output. */
 	base->preferred_base = 1;
diff --git a/pack-objects.h b/pack-objects.h
index d3975e079b..9d88e3e518 100644
--- a/pack-objects.h
+++ b/pack-objects.h
@@ -292,7 +292,7 @@ static inline void oe_set_delta(struct packing_data *pack,
 
 void oe_set_delta_ext(struct packing_data *pack,
 		      struct object_entry *e,
-		      const unsigned char *sha1);
+		      const struct object_id *oid);
 
 static inline struct object_entry *oe_delta_child(
 		const struct packing_data *pack,