diff --git a/odb.c b/odb.c
index ccc6e999e7..88b40c81c0 100644
--- a/odb.c
+++ b/odb.c
@@ -1034,15 +1034,27 @@ int odb_write_object_stream(struct object_database *odb,
 	return odb_source_loose_write_stream(odb->sources, stream, len, oid);
 }
 
-struct object_database *odb_new(struct repository *repo)
+struct object_database *odb_new(struct repository *repo,
+				const char *primary_source,
+				const char *secondary_sources)
 {
 	struct object_database *o = xmalloc(sizeof(*o));
+	char *to_free = NULL;
 
 	memset(o, 0, sizeof(*o));
 	o->repo = repo;
 	o->packfiles = packfile_store_new(o);
 	pthread_mutex_init(&o->replace_mutex, NULL);
 	string_list_init_dup(&o->submodule_source_paths);
+
+	if (!primary_source)
+		primary_source = to_free = xstrfmt("%s/objects", repo->commondir);
+	o->sources = odb_source_new(o, primary_source, true);
+	o->sources_tail = &o->sources->next;
+	o->alternate_db = xstrdup_or_null(secondary_sources);
+
+	free(to_free);
+
 	return o;
 }
 
diff --git a/odb.h b/odb.h
index 99c4d48972..41b3c03027 100644
--- a/odb.h
+++ b/odb.h
@@ -159,7 +159,20 @@ struct object_database {
 	struct string_list submodule_source_paths;
 };
 
-struct object_database *odb_new(struct repository *repo);
+/*
+ * Create a new object database for the given repository.
+ *
+ * If the primary source parameter is set it will override the usual primary
+ * object directory derived from the repository's common directory. The
+ * alternate sources are expected to be a PATH_SEP-separated list of secondary
+ * sources. Note that these alternate sources will be added in addition to, not
+ * instead of, the alternates identified by the primary source.
+ *
+ * Returns the newly created object database.
+ */
+struct object_database *odb_new(struct repository *repo,
+				const char *primary_source,
+				const char *alternate_sources);
 
 /* Free the object database and release all resources. */
 void odb_free(struct object_database *o);
diff --git a/repository.c b/repository.c
index 455c2d279f..5975c8f341 100644
--- a/repository.c
+++ b/repository.c
@@ -52,7 +52,6 @@ static void set_default_hash_algo(struct repository *repo)
 
 void initialize_repository(struct repository *repo)
 {
-	repo->objects = odb_new(repo);
 	repo->remote_state = remote_state_new();
 	repo->parsed_objects = parsed_object_pool_new(repo);
 	ALLOC_ARRAY(repo->index, 1);
@@ -160,29 +159,26 @@ void repo_set_gitdir(struct repository *repo,
 	 * until after xstrdup(root). Then we can free it.
 	 */
 	char *old_gitdir = repo->gitdir;
-	char *objects_path = NULL;
 
 	repo->gitdir = xstrdup(gitfile ? gitfile : root);
 	free(old_gitdir);
 
 	repo_set_commondir(repo, o->commondir);
-	expand_base_dir(&objects_path, o->object_dir,
-			repo->commondir, "objects");
 
-	if (!repo->objects->sources) {
-		repo->objects->sources = odb_source_new(repo->objects,
-							objects_path, true);
-		repo->objects->sources_tail = &repo->objects->sources->next;
-		free(objects_path);
+	if (!repo->objects) {
+		repo->objects = odb_new(repo, o->object_dir, o->alternate_db);
 	} else {
+		char *objects_path = NULL;
+		expand_base_dir(&objects_path, o->object_dir,
+				repo->commondir, "objects");
 		free(repo->objects->sources->path);
 		repo->objects->sources->path = objects_path;
+		free(repo->objects->alternate_db);
+		repo->objects->alternate_db = xstrdup_or_null(o->alternate_db);
 	}
 
 	repo->disable_ref_updates = o->disable_ref_updates;
 
-	free(repo->objects->alternate_db);
-	repo->objects->alternate_db = xstrdup_or_null(o->alternate_db);
 	expand_base_dir(&repo->graft_file, o->graft_file,
 			repo->commondir, "info/grafts");
 	expand_base_dir(&repo->index_file, o->index_file,