diff --git a/archive.c b/archive.c
index 0b7b62af0c3ecee10a26e9bd2d274690604ffcad..e664cdb624253491b8610685c4fca97d32b855fd 100644
--- a/archive.c
+++ b/archive.c
@@ -198,7 +198,7 @@ static int write_directory(struct archiver_context *c)
 	return ret ? -1 : 0;
 }
 
-static int queue_or_write_archive_entry(const unsigned char *sha1,
+static int queue_or_write_archive_entry(const struct object_id *oid,
 		struct strbuf *base, const char *filename,
 		unsigned mode, int stage, void *context)
 {
@@ -224,14 +224,14 @@ static int queue_or_write_archive_entry(const unsigned char *sha1,
 
 		if (check_attr_export_ignore(check))
 			return 0;
-		queue_directory(sha1, base, filename,
+		queue_directory(oid->hash, base, filename,
 				mode, stage, c);
 		return READ_TREE_RECURSIVE;
 	}
 
 	if (write_directory(c))
 		return -1;
-	return write_archive_entry(sha1, base->buf, base->len, filename, mode,
+	return write_archive_entry(oid->hash, base->buf, base->len, filename, mode,
 				   stage, context);
 }
 
@@ -303,7 +303,7 @@ static const struct archiver *lookup_archiver(const char *name)
 	return NULL;
 }
 
-static int reject_entry(const unsigned char *sha1, struct strbuf *base,
+static int reject_entry(const struct object_id *oid, struct strbuf *base,
 			const char *filename, unsigned mode,
 			int stage, void *context)
 {
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 8f4dfb104662baa3f32c350cf58e0f2b797dff29..8eb118201db24152132de85c8577d16163351cc7 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -66,7 +66,7 @@ static int post_checkout_hook(struct commit *old_commit, struct commit *new_comm
 
 }
 
-static int update_some(const unsigned char *sha1, struct strbuf *base,
+static int update_some(const struct object_id *oid, struct strbuf *base,
 		const char *pathname, unsigned mode, int stage, void *context)
 {
 	int len;
@@ -78,7 +78,7 @@ static int update_some(const unsigned char *sha1, struct strbuf *base,
 
 	len = base->len + strlen(pathname);
 	ce = xcalloc(1, cache_entry_size(len));
-	hashcpy(ce->oid.hash, sha1);
+	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, base->buf, base->len);
 	memcpy(ce->name + base->len, pathname, len - base->len);
 	ce->ce_flags = create_ce_flags(0) | CE_UPDATE;
diff --git a/builtin/log.c b/builtin/log.c
index 94ee177d56d6ff9c82b02ebfb2d27cf789527974..32a744bfd2062e93a3b7047eb3bc905ca9dbe047 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -541,7 +541,7 @@ static int show_tag_object(const struct object_id *oid, struct rev_info *rev)
 	return 0;
 }
 
-static int show_tree_object(const unsigned char *sha1,
+static int show_tree_object(const struct object_id *oid,
 		struct strbuf *base,
 		const char *pathname, unsigned mode, int stage, void *context)
 {
diff --git a/builtin/ls-tree.c b/builtin/ls-tree.c
index ef965408e8fc5d80fa9e9daf0264a91abccd978c..c613dd7b8269c537679718dc78eedc6d8c3c9d06 100644
--- a/builtin/ls-tree.c
+++ b/builtin/ls-tree.c
@@ -60,7 +60,7 @@ static int show_recursive(const char *base, int baselen, const char *pathname)
 	return 0;
 }
 
-static int show_tree(const unsigned char *sha1, struct strbuf *base,
+static int show_tree(const struct object_id *oid, struct strbuf *base,
 		const char *pathname, unsigned mode, int stage, void *context)
 {
 	int retval = 0;
@@ -94,7 +94,7 @@ static int show_tree(const unsigned char *sha1, struct strbuf *base,
 			char size_text[24];
 			if (!strcmp(type, blob_type)) {
 				unsigned long size;
-				if (sha1_object_info(sha1, &size) == OBJ_BAD)
+				if (sha1_object_info(oid->hash, &size) == OBJ_BAD)
 					xsnprintf(size_text, sizeof(size_text),
 						  "BAD");
 				else
@@ -103,11 +103,11 @@ static int show_tree(const unsigned char *sha1, struct strbuf *base,
 			} else
 				xsnprintf(size_text, sizeof(size_text), "-");
 			printf("%06o %s %s %7s\t", mode, type,
-			       find_unique_abbrev(sha1, abbrev),
+			       find_unique_abbrev(oid->hash, abbrev),
 			       size_text);
 		} else
 			printf("%06o %s %s\t", mode, type,
-			       find_unique_abbrev(sha1, abbrev));
+			       find_unique_abbrev(oid->hash, abbrev));
 	}
 	baselen = base->len;
 	strbuf_addstr(base, pathname);
diff --git a/merge-recursive.c b/merge-recursive.c
index 6ff971f9a2a8e251b8762d75214697698e2d1ce6..c886f2e9cd41d102a345a4a8392a4c9cd765db14 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -335,7 +335,7 @@ struct tree *write_tree_from_memory(struct merge_options *o)
 	return result;
 }
 
-static int save_files_dirs(const unsigned char *sha1,
+static int save_files_dirs(const struct object_id *oid,
 		struct strbuf *base, const char *path,
 		unsigned int mode, int stage, void *context)
 {
diff --git a/tree.c b/tree.c
index b224115e0f4d61368560eba406a04f0259b7c4f0..1a0f03f5207a4cd85da5540edc5be593ff37e829 100644
--- a/tree.c
+++ b/tree.c
@@ -10,7 +10,7 @@
 const char *tree_type = "tree";
 
 static int read_one_entry_opt(struct index_state *istate,
-			      const unsigned char *sha1,
+			      const struct object_id *oid,
 			      const char *base, int baselen,
 			      const char *pathname,
 			      unsigned mode, int stage, int opt)
@@ -31,16 +31,16 @@ static int read_one_entry_opt(struct index_state *istate,
 	ce->ce_namelen = baselen + len;
 	memcpy(ce->name, base, baselen);
 	memcpy(ce->name + baselen, pathname, len+1);
-	hashcpy(ce->oid.hash, sha1);
+	oidcpy(&ce->oid, oid);
 	return add_index_entry(istate, ce, opt);
 }
 
-static int read_one_entry(const unsigned char *sha1, struct strbuf *base,
+static int read_one_entry(const struct object_id *oid, struct strbuf *base,
 			  const char *pathname, unsigned mode, int stage,
 			  void *context)
 {
 	struct index_state *istate = context;
-	return read_one_entry_opt(istate, sha1, base->buf, base->len, pathname,
+	return read_one_entry_opt(istate, oid, base->buf, base->len, pathname,
 				  mode, stage,
 				  ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
 }
@@ -49,12 +49,12 @@ static int read_one_entry(const unsigned char *sha1, struct strbuf *base,
  * This is used when the caller knows there is no existing entries at
  * the stage that will conflict with the entry being added.
  */
-static int read_one_entry_quick(const unsigned char *sha1, struct strbuf *base,
+static int read_one_entry_quick(const struct object_id *oid, struct strbuf *base,
 				const char *pathname, unsigned mode, int stage,
 				void *context)
 {
 	struct index_state *istate = context;
-	return read_one_entry_opt(istate, sha1, base->buf, base->len, pathname,
+	return read_one_entry_opt(istate, oid, base->buf, base->len, pathname,
 				  mode, stage,
 				  ADD_CACHE_JUST_APPEND);
 }
@@ -83,7 +83,7 @@ static int read_tree_1(struct tree *tree, struct strbuf *base,
 				continue;
 		}
 
-		switch (fn(entry.oid->hash, base,
+		switch (fn(entry.oid, base,
 			   entry.path, entry.mode, stage, context)) {
 		case 0:
 			continue;
diff --git a/tree.h b/tree.h
index 744e6dc2ac883adfa0e079f5f84f45a45e22b59d..e2a80be4ef87e35d895e8591a0f8a75df347d347 100644
--- a/tree.h
+++ b/tree.h
@@ -27,7 +27,7 @@ void free_tree_buffer(struct tree *tree);
 struct tree *parse_tree_indirect(const struct object_id *oid);
 
 #define READ_TREE_RECURSIVE 1
-typedef int (*read_tree_fn_t)(const unsigned char *, struct strbuf *, const char *, unsigned int, int, void *);
+typedef int (*read_tree_fn_t)(const struct object_id *, struct strbuf *, const char *, unsigned int, int, void *);
 
 extern int read_tree_recursive(struct tree *tree,
 			       const char *base, int baselen,