diff --git a/src/iperf_api.c b/src/iperf_api.c
index 4765d4e97..a296780a1 100644
--- a/src/iperf_api.c
+++ b/src/iperf_api.c
@@ -892,7 +892,7 @@ void
 iperf_on_test_start(struct iperf_test *test)
 {
     if (test->json_output) {
-	cJSON_AddItemToObject(test->json_start, "test_start", iperf_json_printf("protocol: %s  num_streams: %d  blksize: %d  omit: %d  duration: %d  bytes: %d  blocks: %d  reverse: %d  tos: %d  target_bitrate: %d bidir: %d fqrate: %d", test->protocol->name, (int64_t) test->num_streams, (int64_t) test->settings->blksize, (int64_t) test->omit, (int64_t) test->duration, (int64_t) test->settings->bytes, (int64_t) test->settings->blocks, test->reverse?(int64_t)1:(int64_t)0, (int64_t) test->settings->tos, (int64_t) test->settings->rate, (int64_t) test->bidirectional, (uint64_t) test->settings->fqrate));
+	cJSON_AddItemToObject(test->json_start, "test_start", iperf_json_printf("protocol: %s  num_streams: %d  blksize: %d  omit: %d  duration: %d  bytes: %d  blocks: %d  reverse: %d  tos: %d  target_bitrate: %d bidir: %d fqrate: %d interval: %f", test->protocol->name, (int64_t) test->num_streams, (int64_t) test->settings->blksize, (int64_t) test->omit, (int64_t) test->duration, (int64_t) test->settings->bytes, (int64_t) test->settings->blocks, test->reverse?(int64_t)1:(int64_t)0, (int64_t) test->settings->tos, (int64_t) test->settings->rate, (int64_t) test->bidirectional, (uint64_t) test->settings->fqrate, test->stats_interval));
     } else {
 	if (test->verbose) {
 	    if (test->settings->bytes)