diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index ae63f7c3d3..0b562693b1 100644
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -2275,12 +2275,13 @@ static void *_sip_tcp_helper_thread(struct sip_pvt *pvt, struct ast_tcptls_sessi
 		parse_copy(&reqcpy, &req);
 		if (sscanf(get_header(&reqcpy, "Content-Length"), "%30d", &cl)) {
 			while (cl > 0) {
+				size_t bytes_read;
 				ast_mutex_lock(&tcptls_session->lock);
-				if (!fread(buf, MIN(sizeof(buf) - 1, cl), 1, tcptls_session->f)) {
+				if (!(bytes_read = fread(buf, MIN(sizeof(buf) - 1, cl), 1, tcptls_session->f))) {
 					ast_mutex_unlock(&tcptls_session->lock);
 					goto cleanup;
 				}
-				buf[sizeof(buf)-1] = '\0';
+				buf[bytes_read] = '\0';
 				ast_mutex_unlock(&tcptls_session->lock);
 				if (me->stop)
 					goto cleanup;