diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 010ef811b6..f8f930380d 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -129,7 +129,7 @@ static struct reftable_stack *stack_for(struct reftable_ref_store *store,
 				    store->base.repo->commondir, wtname_buf.buf);
 
 			store->err = reftable_new_stack(&stack, wt_dir.buf,
-							store->write_options);
+							&store->write_options);
 			assert(store->err != REFTABLE_API_ERROR);
 			strmap_put(&store->worktree_stacks, wtname_buf.buf, stack);
 		}
@@ -263,7 +263,7 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 	}
 	strbuf_addstr(&path, "/reftable");
 	refs->err = reftable_new_stack(&refs->main_stack, path.buf,
-				       refs->write_options);
+				       &refs->write_options);
 	if (refs->err)
 		goto done;
 
@@ -280,7 +280,7 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 		strbuf_addf(&path, "%s/reftable", gitdir);
 
 		refs->err = reftable_new_stack(&refs->worktree_stack, path.buf,
-					       refs->write_options);
+					       &refs->write_options);
 		if (refs->err)
 			goto done;
 	}
diff --git a/reftable/dump.c b/reftable/dump.c
index 9c770a10cc..586f3eb288 100644
--- a/reftable/dump.c
+++ b/reftable/dump.c
@@ -29,7 +29,7 @@ static int compact_stack(const char *stackdir)
 	struct reftable_stack *stack = NULL;
 	struct reftable_write_options opts = { 0 };
 
-	int err = reftable_new_stack(&stack, stackdir, opts);
+	int err = reftable_new_stack(&stack, stackdir, &opts);
 	if (err < 0)
 		goto done;
 
diff --git a/reftable/reftable-stack.h b/reftable/reftable-stack.h
index 9c8e4eef49..c15632c401 100644
--- a/reftable/reftable-stack.h
+++ b/reftable/reftable-stack.h
@@ -29,7 +29,7 @@ struct reftable_stack;
  *  stored in 'dir'. Typically, this should be .git/reftables.
  */
 int reftable_new_stack(struct reftable_stack **dest, const char *dir,
-		       struct reftable_write_options opts);
+		       const struct reftable_write_options *opts);
 
 /* returns the update_index at which a next table should be written. */
 uint64_t reftable_stack_next_update_index(struct reftable_stack *st);
diff --git a/reftable/reftable-writer.h b/reftable/reftable-writer.h
index b601a69a40..03df3a4963 100644
--- a/reftable/reftable-writer.h
+++ b/reftable/reftable-writer.h
@@ -88,7 +88,7 @@ struct reftable_stats {
 struct reftable_writer *
 reftable_new_writer(ssize_t (*writer_func)(void *, const void *, size_t),
 		    int (*flush_func)(void *),
-		    void *writer_arg, struct reftable_write_options *opts);
+		    void *writer_arg, const struct reftable_write_options *opts);
 
 /* Set the range of update indices for the records we will add. When writing a
    table into a stack, the min should be at least
diff --git a/reftable/stack.c b/reftable/stack.c
index 54e7473f3a..d2e68be7e8 100644
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -54,12 +54,15 @@ static int reftable_fd_flush(void *arg)
 }
 
 int reftable_new_stack(struct reftable_stack **dest, const char *dir,
-		       struct reftable_write_options opts)
+		       const struct reftable_write_options *_opts)
 {
 	struct reftable_stack *p = reftable_calloc(1, sizeof(*p));
 	struct strbuf list_file_name = STRBUF_INIT;
+	struct reftable_write_options opts = {0};
 	int err = 0;
 
+	if (_opts)
+		opts = *_opts;
 	if (opts.hash_id == 0)
 		opts.hash_id = GIT_SHA1_FORMAT_ID;
 
@@ -1438,7 +1441,7 @@ int reftable_stack_print_directory(const char *stackdir, uint32_t hash_id)
 	struct reftable_merged_table *merged = NULL;
 	struct reftable_table table = { NULL };
 
-	int err = reftable_new_stack(&stack, stackdir, opts);
+	int err = reftable_new_stack(&stack, stackdir, &opts);
 	if (err < 0)
 		goto done;
 
diff --git a/reftable/stack_test.c b/reftable/stack_test.c
index e17ad4dc62..d15f11d712 100644
--- a/reftable/stack_test.c
+++ b/reftable/stack_test.c
@@ -163,7 +163,7 @@ static void test_reftable_stack_add_one(void)
 	};
 	struct reftable_ref_record dest = { NULL };
 	struct stat stat_result = { 0 };
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st, &write_test_ref, &ref);
@@ -232,10 +232,10 @@ static void test_reftable_stack_uptodate(void)
 	/* simulate multi-process access to the same stack
 	   by creating two stacks for the same directory.
 	 */
-	err = reftable_new_stack(&st1, dir, opts);
+	err = reftable_new_stack(&st1, dir, &opts);
 	EXPECT_ERR(err);
 
-	err = reftable_new_stack(&st2, dir, opts);
+	err = reftable_new_stack(&st2, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st1, &write_test_ref, &ref1);
@@ -270,7 +270,7 @@ static void test_reftable_stack_transaction_api(void)
 	};
 	struct reftable_ref_record dest = { NULL };
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	reftable_addition_destroy(add);
@@ -304,7 +304,7 @@ static void test_reftable_stack_transaction_api_performs_auto_compaction(void)
 	struct reftable_stack *st = NULL;
 	int i, n = 20, err;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i <= n; i++) {
@@ -365,7 +365,7 @@ static void test_reftable_stack_auto_compaction_fails_gracefully(void)
 	char *dir = get_tmp_dir(__LINE__);
 	int err;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st, write_test_ref, &ref);
@@ -418,7 +418,7 @@ static void test_reftable_stack_update_index_check(void)
 		.value.symref = "master",
 	};
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st, &write_test_ref, &ref1);
@@ -437,7 +437,7 @@ static void test_reftable_stack_lock_failure(void)
 	struct reftable_stack *st = NULL;
 	int err, i;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 	for (i = -1; i != REFTABLE_EMPTY_TABLE_ERROR; i--) {
 		err = reftable_stack_add(st, &write_error, &i);
@@ -465,7 +465,7 @@ static void test_reftable_stack_add(void)
 	struct stat stat_result;
 	int N = ARRAY_SIZE(refs);
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i < N; i++) {
@@ -575,7 +575,7 @@ static void test_reftable_stack_log_normalize(void)
 		.update_index = 1,
 	};
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	input.value.update.message = "one\ntwo";
@@ -617,7 +617,7 @@ static void test_reftable_stack_tombstone(void)
 	struct reftable_ref_record dest = { NULL };
 	struct reftable_log_record log_dest = { NULL };
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	/* even entries add the refs, odd entries delete them. */
@@ -701,18 +701,18 @@ static void test_reftable_stack_hash_id(void)
 	struct reftable_stack *st_default = NULL;
 	struct reftable_ref_record dest = { NULL };
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st, &write_test_ref, &ref);
 	EXPECT_ERR(err);
 
 	/* can't read it with the wrong hash ID. */
-	err = reftable_new_stack(&st32, dir, opts32);
+	err = reftable_new_stack(&st32, dir, &opts32);
 	EXPECT(err == REFTABLE_FORMAT_ERROR);
 
 	/* check that we can read it back with default opts too. */
-	err = reftable_new_stack(&st_default, dir, opts_default);
+	err = reftable_new_stack(&st_default, dir, &opts_default);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_read_ref(st_default, "master", &dest);
@@ -756,7 +756,7 @@ static void test_reflog_expire(void)
 	};
 	struct reftable_log_record log = { NULL };
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 1; i <= N; i++) {
@@ -825,13 +825,13 @@ static void test_empty_add(void)
 	char *dir = get_tmp_dir(__LINE__);
 	struct reftable_stack *st2 = NULL;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st, &write_nothing, NULL);
 	EXPECT_ERR(err);
 
-	err = reftable_new_stack(&st2, dir, opts);
+	err = reftable_new_stack(&st2, dir, &opts);
 	EXPECT_ERR(err);
 	clear_dir(dir);
 	reftable_stack_destroy(st);
@@ -858,7 +858,7 @@ static void test_reftable_stack_auto_compaction(void)
 	int err, i;
 	int N = 100;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i < N; i++) {
@@ -894,7 +894,7 @@ static void test_reftable_stack_add_performs_auto_compaction(void)
 	char *dir = get_tmp_dir(__LINE__);
 	int err, i, n = 20;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i <= n; i++) {
@@ -942,7 +942,7 @@ static void test_reftable_stack_compaction_concurrent(void)
 	int err, i;
 	int N = 3;
 
-	err = reftable_new_stack(&st1, dir, opts);
+	err = reftable_new_stack(&st1, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i < N; i++) {
@@ -959,7 +959,7 @@ static void test_reftable_stack_compaction_concurrent(void)
 		EXPECT_ERR(err);
 	}
 
-	err = reftable_new_stack(&st2, dir, opts);
+	err = reftable_new_stack(&st2, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_compact_all(st1, NULL);
@@ -991,7 +991,7 @@ static void test_reftable_stack_compaction_concurrent_clean(void)
 	int err, i;
 	int N = 3;
 
-	err = reftable_new_stack(&st1, dir, opts);
+	err = reftable_new_stack(&st1, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i < N; i++) {
@@ -1008,7 +1008,7 @@ static void test_reftable_stack_compaction_concurrent_clean(void)
 		EXPECT_ERR(err);
 	}
 
-	err = reftable_new_stack(&st2, dir, opts);
+	err = reftable_new_stack(&st2, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_compact_all(st1, NULL);
@@ -1017,7 +1017,7 @@ static void test_reftable_stack_compaction_concurrent_clean(void)
 	unclean_stack_close(st1);
 	unclean_stack_close(st2);
 
-	err = reftable_new_stack(&st3, dir, opts);
+	err = reftable_new_stack(&st3, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_clean(st3);
diff --git a/reftable/writer.c b/reftable/writer.c
index 10eccaaa07..4cc6e2ebd8 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -122,20 +122,25 @@ static struct strbuf reftable_empty_strbuf = STRBUF_INIT;
 struct reftable_writer *
 reftable_new_writer(ssize_t (*writer_func)(void *, const void *, size_t),
 		    int (*flush_func)(void *),
-		    void *writer_arg, struct reftable_write_options *opts)
+		    void *writer_arg, const struct reftable_write_options *_opts)
 {
 	struct reftable_writer *wp = reftable_calloc(1, sizeof(*wp));
-	strbuf_init(&wp->block_writer_data.last_key, 0);
-	options_set_defaults(opts);
-	if (opts->block_size >= (1 << 24)) {
+	struct reftable_write_options opts = {0};
+
+	if (_opts)
+		opts = *_opts;
+	options_set_defaults(&opts);
+	if (opts.block_size >= (1 << 24)) {
 		/* TODO - error return? */
 		abort();
 	}
+
+	strbuf_init(&wp->block_writer_data.last_key, 0);
 	wp->last_key = reftable_empty_strbuf;
-	REFTABLE_CALLOC_ARRAY(wp->block, opts->block_size);
+	REFTABLE_CALLOC_ARRAY(wp->block, opts.block_size);
 	wp->write = writer_func;
 	wp->write_arg = writer_arg;
-	wp->opts = *opts;
+	wp->opts = opts;
 	wp->flush = flush_func;
 	writer_reinit_block_writer(wp, BLOCK_TYPE_REF);