diff --git a/src/iperf_server_api.c b/src/iperf_server_api.c
index 79ae695..9a01b54 100644
--- a/src/iperf_server_api.c
+++ b/src/iperf_server_api.c
@@ -466,6 +466,7 @@
     }
     if (test->congestion_used != NULL) {
         free(test->congestion_used);
+	test->congestion_used = NULL;
     }
     if (test->timer != NULL) {
         tmr_cancel(test->timer);