diff --git a/src/device/mouse_microtouch_touchscreen.c b/src/device/mouse_microtouch_touchscreen.c
index 0aa0ce727..ce87a4b68 100644
--- a/src/device/mouse_microtouch_touchscreen.c
+++ b/src/device/mouse_microtouch_touchscreen.c
@@ -322,6 +322,8 @@ void
 mtouch_write_to_host(void *priv)
 {
     mouse_microtouch_t *dev = (mouse_microtouch_t *) priv;
+    if (dev->serial == NULL)
+        goto no_write_to_machine;
     if ((dev->serial->type >= SERIAL_16550) && dev->serial->fifo_enabled) {
         if (fifo_get_full(dev->serial->rcvr_fifo)) {
             goto no_write_to_machine;
diff --git a/src/device/mouse_serial.c b/src/device/mouse_serial.c
index 08aee09d8..afc662a19 100644
--- a/src/device/mouse_serial.c
+++ b/src/device/mouse_serial.c
@@ -142,7 +142,8 @@ sermouse_transmit_byte(mouse_t *dev, int do_next)
     if (dev->buf_pos == 0)
         dev->acc_time = 0.0;
 
-    serial_write_fifo(dev->serial, dev->buf[dev->buf_pos]);
+    if (dev->serial)
+        serial_write_fifo(dev->serial, dev->buf[dev->buf_pos]);
 
     if (do_next) {
         dev->buf_pos = (dev->buf_pos + 1) % dev->buf_len;
diff --git a/src/network/net_modem.c b/src/network/net_modem.c
index 6addec352..bb312ec31 100644
--- a/src/network/net_modem.c
+++ b/src/network/net_modem.c
@@ -434,7 +434,7 @@ host_to_modem_cb(void *priv)
 {
     modem_t *modem = (modem_t *) priv;
 
-    if (modem->in_warmup)
+    if (modem->in_warmup || (modem->serial == NULL))
         goto no_write_to_machine;
 
     if ((modem->serial->type >= SERIAL_16550) && modem->serial->fifo_enabled) {
@@ -621,10 +621,12 @@ modem_enter_idle_state(modem_t *modem)
         }
     }
 
-    serial_set_cts(modem->serial, 1);
-    serial_set_dsr(modem->serial, 1);
-    serial_set_dcd(modem->serial, (!modem->dcdmode ? 1 : 0));
-    serial_set_ri(modem->serial, 0);
+    if (modem->serial != NULL) {
+        serial_set_cts(modem->serial, 1);
+        serial_set_dsr(modem->serial, 1);
+        serial_set_dcd(modem->serial, (!modem->dcdmode ? 1 : 0));
+        serial_set_ri(modem->serial, 0);
+    }
 }
 
 void
@@ -640,8 +642,11 @@ modem_enter_connected_state(modem_t *modem)
     plat_netsocket_close(modem->serversocket);
     modem->serversocket = -1;
     memset(&modem->telClient, 0, sizeof(modem->telClient));
-    serial_set_dcd(modem->serial, 1);
-    serial_set_ri(modem->serial, 0);
+
+    if (modem->serial != NULL) {
+        serial_set_dcd(modem->serial, 1);
+        serial_set_ri(modem->serial, 0);
+    }
 }
 
 void
@@ -1391,7 +1396,8 @@ modem_cmdpause_timer_callback(void *priv)
             } else {
                 modem->ringing = true;
                 modem_send_res(modem, ResRING);
-                serial_set_ri(modem->serial, !serial_get_ri(modem->serial));
+                if (modem->serial != NULL)
+                    serial_set_ri(modem->serial, !serial_get_ri(modem->serial));
                 modem->ringtimer            = 3000;
                 modem->reg[MREG_RING_COUNT] = 0;
             }
@@ -1405,7 +1411,8 @@ modem_cmdpause_timer_callback(void *priv)
                 return;
             }
             modem_send_res(modem, ResRING);
-            serial_set_ri(modem->serial, !serial_get_ri(modem->serial));
+            if (modem->serial != NULL)
+                serial_set_ri(modem->serial, !serial_get_ri(modem->serial));
 
             modem->ringtimer = 3000;
         }