diff --git a/builtin/merge.c b/builtin/merge.c
index 592cb19caf..5f79fc5fd7 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -728,8 +728,9 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
 			die(_("unable to write %s"), get_index_file());
 		return clean ? 0 : 1;
 	} else {
-		return try_merge_command(strategy, xopts_nr, xopts,
-						common, head_arg, remoteheads);
+		return try_merge_command(the_repository,
+					 strategy, xopts_nr, xopts,
+					 common, head_arg, remoteheads);
 	}
 }
 
@@ -1470,7 +1471,8 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 			goto done;
 		}
 
-		if (checkout_fast_forward(&head_commit->object.oid,
+		if (checkout_fast_forward(the_repository,
+					  &head_commit->object.oid,
 					  &commit->object.oid,
 					  overwrite_ignore)) {
 			ret = 1;
diff --git a/builtin/pull.c b/builtin/pull.c
index 681c127a07..33b7100837 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -562,7 +562,9 @@ static int pull_into_void(const struct object_id *merge_head,
 	 * index/worktree changes that the user already made on the unborn
 	 * branch.
 	 */
-	if (checkout_fast_forward(the_hash_algo->empty_tree, merge_head, 0))
+	if (checkout_fast_forward(the_repository,
+				  the_hash_algo->empty_tree,
+				  merge_head, 0))
 		return 1;
 
 	if (update_ref("initial pull", "HEAD", merge_head, curr_head, 0, UPDATE_REFS_DIE_ON_ERR))
@@ -915,7 +917,8 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 			"fast-forwarding your working tree from\n"
 			"commit %s."), oid_to_hex(&orig_head));
 
-		if (checkout_fast_forward(&orig_head, &curr_head, 0))
+		if (checkout_fast_forward(the_repository, &orig_head,
+					  &curr_head, 0))
 			die(_("Cannot fast-forward your working tree.\n"
 				"After making sure that you saved anything precious from\n"
 				"$ git diff %s\n"
diff --git a/cache.h b/cache.h
index 260e4ee44a..49fe83331c 100644
--- a/cache.h
+++ b/cache.h
@@ -1716,10 +1716,12 @@ extern struct startup_info *startup_info;
 
 /* merge.c */
 struct commit_list;
-int try_merge_command(const char *strategy, size_t xopts_nr,
+int try_merge_command(struct repository *r,
+		const char *strategy, size_t xopts_nr,
 		const char **xopts, struct commit_list *common,
 		const char *head_arg, struct commit_list *remotes);
-int checkout_fast_forward(const struct object_id *from,
+int checkout_fast_forward(struct repository *r,
+			  const struct object_id *from,
 			  const struct object_id *to,
 			  int overwrite_ignore);
 
diff --git a/merge.c b/merge.c
index e30e03fb84..91008f7602 100644
--- a/merge.c
+++ b/merge.c
@@ -14,7 +14,8 @@ static const char *merge_argument(struct commit *commit)
 	return oid_to_hex(commit ? &commit->object.oid : the_hash_algo->empty_tree);
 }
 
-int try_merge_command(const char *strategy, size_t xopts_nr,
+int try_merge_command(struct repository *r,
+		      const char *strategy, size_t xopts_nr,
 		      const char **xopts, struct commit_list *common,
 		      const char *head_arg, struct commit_list *remotes)
 {
@@ -35,15 +36,16 @@ int try_merge_command(const char *strategy, size_t xopts_nr,
 	ret = run_command_v_opt(args.argv, RUN_GIT_CMD);
 	argv_array_clear(&args);
 
-	discard_cache();
-	if (read_cache() < 0)
+	discard_index(r->index);
+	if (read_index(r->index) < 0)
 		die(_("failed to read the cache"));
-	resolve_undo_clear();
+	resolve_undo_clear_index(r->index);
 
 	return ret;
 }
 
-int checkout_fast_forward(const struct object_id *head,
+int checkout_fast_forward(struct repository *r,
+			  const struct object_id *head,
 			  const struct object_id *remote,
 			  int overwrite_ignore)
 {
@@ -54,7 +56,7 @@ int checkout_fast_forward(const struct object_id *head,
 	struct dir_struct dir;
 	struct lock_file lock_file = LOCK_INIT;
 
-	refresh_cache(REFRESH_QUIET);
+	refresh_index(r->index, REFRESH_QUIET, NULL, NULL, NULL);
 
 	if (hold_locked_index(&lock_file, LOCK_REPORT_ON_ERROR) < 0)
 		return -1;
@@ -86,8 +88,8 @@ int checkout_fast_forward(const struct object_id *head,
 	}
 
 	opts.head_idx = 1;
-	opts.src_index = &the_index;
-	opts.dst_index = &the_index;
+	opts.src_index = r->index;
+	opts.dst_index = r->index;
 	opts.update = 1;
 	opts.verbose_update = 1;
 	opts.merge = 1;
@@ -101,7 +103,7 @@ int checkout_fast_forward(const struct object_id *head,
 	}
 	clear_unpack_trees_porcelain(&opts);
 
-	if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
+	if (write_locked_index(r->index, &lock_file, COMMIT_LOCK))
 		return error(_("unable to write new index file"));
 	return 0;
 }
diff --git a/sequencer.c b/sequencer.c
index 84bf598c3e..47d0e7b0bd 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -470,8 +470,8 @@ static int fast_forward_to(const struct object_id *to, const struct object_id *f
 	struct strbuf sb = STRBUF_INIT;
 	struct strbuf err = STRBUF_INIT;
 
-	read_cache();
-	if (checkout_fast_forward(from, to, 1))
+	read_index(&the_index);
+	if (checkout_fast_forward(the_repository, from, to, 1))
 		return -1; /* the callee should have complained already */
 
 	strbuf_addf(&sb, _("%s: fast-forward"), _(action_name(opts)));
@@ -1798,7 +1798,7 @@ static int do_pick_commit(enum todo_command command, struct commit *commit,
 
 		commit_list_insert(base, &common);
 		commit_list_insert(next, &remotes);
-		res |= try_merge_command(opts->strategy,
+		res |= try_merge_command(the_repository, opts->strategy,
 					 opts->xopts_nr, (const char **)opts->xopts,
 					common, oid_to_hex(&head), remotes);
 		free_commit_list(common);
