diff -Naur a/res/res_rtp_asterisk.c b/res/res_rtp_asterisk.c
--- a/res/res_rtp_asterisk.c	2015-08-24 11:29:13.000000000 +0200
+++ b/res/res_rtp_asterisk.c	2015-08-24 14:46:07.029134437 +0200
@@ -3130,8 +3130,9 @@
 static int ast_rtp_raw_write(struct ast_rtp_instance *instance, struct ast_frame *frame, int codec)
 {
 	struct ast_rtp *rtp = ast_rtp_instance_get_data(instance);
-	int pred, mark = 0;
+	unsigned int pred, mark = 0;
 	unsigned int ms = calc_txstamp(rtp, &frame->delivery);
+	int diff = 0;
 	struct ast_sockaddr remote_address = { {0,} };
 	int rate = rtp_get_rate(frame->subclass.format) / 1000;
 
@@ -3148,15 +3149,19 @@
 
 		/* Re-calculate last TS */
 		rtp->lastts = rtp->lastts + ms * rate;
+		diff = rtp->lastts - pred;
+		ast_debug(3, "lassts: %u, ms: %u, diff: %d, rate: %d, pred: %u\n", rtp->lastts, ms, diff, rate, pred);
 		if (ast_tvzero(frame->delivery)) {
 			/* If this isn't an absolute delivery time, Check if it is close to our prediction,
 			   and if so, go with our prediction */
-			if (abs((int)rtp->lastts - pred) < MAX_TIMESTAMP_SKEW) {
+			if (abs(diff) < MAX_TIMESTAMP_SKEW) {
 				rtp->lastts = pred;
 			} else {
 				ast_debug(3, "Difference is %d, ms is %u\n", abs((int)rtp->lastts - pred), ms);
 				mark = 1;
 			}
+		} else {
+		    ast_debug(3, "ast_tvzero(frame->delivery) is false\n");
 		}
 	} else if (frame->frametype == AST_FRAME_VIDEO) {
 		mark = frame->subclass.frame_ending;