diff --git a/H316/h316_udp.c b/H316/h316_udp.c
index 42f30ebd..e17a448d 100644
--- a/H316/h316_udp.c
+++ b/H316/h316_udp.c
@@ -359,7 +359,7 @@ int32 udp_receive_packet (int32 link, UDP_PACKET *ppkt)
   // of the checking for valid packets, unexpected packets, duplicate or out of
   // sequence packets.  That's strictly the caller's problem!
   size_t pktsiz;
-  uint8 *pbuf;
+  const uint8 *pbuf;
   t_stat ret;
 
   udp_lines[link].rcve = TRUE;          // Enable receiver
diff --git a/sim_tmxr.c b/sim_tmxr.c
index 7fc45482..42af7abd 100644
--- a/sim_tmxr.c
+++ b/sim_tmxr.c
@@ -1572,12 +1572,12 @@ return val;
        NULL, but success (SCPE_OK) is returned
 */
 
-t_stat tmxr_get_packet_ln (TMLN *lp, uint8 **pbuf, size_t *psize)
+t_stat tmxr_get_packet_ln (TMLN *lp, const uint8 **pbuf, size_t *psize)
 {
 return tmxr_get_packet_ln_ex (lp, pbuf, psize, 0);
 }
 
-t_stat tmxr_get_packet_ln_ex (TMLN *lp, uint8 **pbuf, size_t *psize, uint8 frame_byte)
+t_stat tmxr_get_packet_ln_ex (TMLN *lp, const uint8 **pbuf, size_t *psize, uint8 frame_byte)
 {
 int32 c;
 size_t pktsize;
diff --git a/sim_tmxr.h b/sim_tmxr.h
index 4c437a71..b6f3a4b0 100644
--- a/sim_tmxr.h
+++ b/sim_tmxr.h
@@ -185,8 +185,8 @@ int32 tmxr_poll_conn (TMXR *mp);
 t_stat tmxr_reset_ln (TMLN *lp);
 t_stat tmxr_detach_ln (TMLN *lp);
 int32 tmxr_getc_ln (TMLN *lp);
-t_stat tmxr_get_packet_ln (TMLN *lp, uint8 **pbuf, size_t *psize);
-t_stat tmxr_get_packet_ln_ex (TMLN *lp, uint8 **pbuf, size_t *psize, uint8 frame_byte);
+t_stat tmxr_get_packet_ln (TMLN *lp, const uint8 **pbuf, size_t *psize);
+t_stat tmxr_get_packet_ln_ex (TMLN *lp, const uint8 **pbuf, size_t *psize, uint8 frame_byte);
 void tmxr_poll_rx (TMXR *mp);
 t_stat tmxr_putc_ln (TMLN *lp, int32 chr);
 t_stat tmxr_put_packet_ln (TMLN *lp, const uint8 *buf, size_t size);