diff --git a/reftable/writer.c b/reftable/writer.c
index 0133b64975..1bd4aa388b 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -152,16 +152,16 @@ int reftable_writer_new(struct reftable_writer **out,
 	struct reftable_write_options opts = {0};
 	struct reftable_writer *wp;
 
-	wp = reftable_calloc(1, sizeof(*wp));
-	if (!wp)
-		return REFTABLE_OUT_OF_MEMORY_ERROR;
-
 	if (_opts)
 		opts = *_opts;
 	options_set_defaults(&opts);
 	if (opts.block_size >= (1 << 24))
 		return REFTABLE_API_ERROR;
 
+	wp = reftable_calloc(1, sizeof(*wp));
+	if (!wp)
+		return REFTABLE_OUT_OF_MEMORY_ERROR;
+
 	reftable_buf_init(&wp->block_writer_data.last_key);
 	reftable_buf_init(&wp->last_key);
 	reftable_buf_init(&wp->scratch);