diff --git a/openbsc/tests/mgcp/mgcp_test.c b/openbsc/tests/mgcp/mgcp_test.c
index fdb1890..498a1d8 100644
--- a/openbsc/tests/mgcp/mgcp_test.c
+++ b/openbsc/tests/mgcp/mgcp_test.c
@@ -28,6 +28,7 @@
 #include <limits.h>
 #include <dlfcn.h>
 #include <time.h>
+#include <math.h>
 
 char *strline_r(char *str, char **saveptr);
 
@@ -800,7 +801,7 @@
 	for (i = 0; i < ARRAY_SIZE(test_rtp_packets1); ++i) {
 		struct rtp_packet_info *info = test_rtp_packets1 + i;
 
-		force_monotonic_time_us = 1000000ULL * info->txtime;
+		force_monotonic_time_us = round(1000000.0 * info->txtime);
 
 		OSMO_ASSERT(info->len <= sizeof(buffer));
 		OSMO_ASSERT(info->len >= 0);