diff --git a/res/res_rtp_asterisk.c b/res/res_rtp_asterisk.c
index e5bef24258..5227e94fff 100644
--- a/res/res_rtp_asterisk.c
+++ b/res/res_rtp_asterisk.c
@@ -39,6 +39,7 @@
 #include <sys/time.h>
 #include <signal.h>
 #include <fcntl.h>
+#include <math.h>
 
 #ifdef HAVE_OPENSSL
 #include <openssl/opensslconf.h>