diff --git a/src/main.c b/src/main.c
index 1892de0e5..dc34b536a 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1165,17 +1165,19 @@ int main(int argc, char * argv [])
   }
 
   // Divide the port string into tokens separated by colon(s).
-  // There are four ways a port string can be presented:
+  // There are several ways a port string can be presented:
   // 1) -P [serialadapter]
   // 2) -P [serialadapter]:[sernum]
   // 3) -P [usbvid]:[usbpid]
   // 4) -P [usbvid]:[usbpid]:[sernum]
+  // 5) -P usb:[usbvid]:[usbpid]
+  // 6) -P usb:[usbvid]:[usbpid]:[sernum]
   if(pgm->conntype == CONNTYPE_SERIAL) {
     char *portdup = cfg_strdup(__func__, port);
-    char port_tok[3][256];
+    char port_tok[4][256];
     memset(port_tok, 0, sizeof(port_tok));
     char *tok = strtok(portdup, ":");
-    for (int i = 0; i < 3; i++) {
+    for (int i = 0; i < 4; i++) {
       if (!tok)
         break;
       strncpy(port_tok[i], tok, sizeof port_tok[i] - 1);
@@ -1195,13 +1197,23 @@ int main(int argc, char * argv [])
       }
     } else {
       // Port or usb vid/pid
+      char *vidptr, *pidptr, *snptr = NULL;
+      if (str_caseeq(port_tok[0], "usb")) {
+       vidptr = port_tok[1];
+       pidptr = port_tok[2];
+       snptr  = port_tok[3];
+      } else {
+       vidptr = port_tok[0];
+       pidptr = port_tok[1];
+       snptr  = port_tok[2];
+      }
       int vid, pid;
-      if (sscanf(port_tok[0], "%x", &vid) > 0 && sscanf(port_tok[1], "%x", &pid) > 0) {
-        if(setport_from_vid_pid(&port, vid, pid, port_tok[2]) < 0) {
-          if (port_tok[2][0])
-            pmsg_warning("serial adapter with USB VID %s and PID %s and serial number %s not found\n", port_tok[0], port_tok[1], port_tok[2]);
+      if (sscanf(vidptr, "%x", &vid) > 0 && sscanf(pidptr, "%x", &pid) > 0) {
+        if(setport_from_vid_pid(&port, vid, pid, snptr) < 0) {
+          if (snptr[0])
+            pmsg_warning("serial adapter with USB VID %s and PID %s and serial number %s not found\n", vidptr, pidptr, snptr);
           else
-            pmsg_warning("serial adapter with USB VID %s and PID %s not found\n", port_tok[0], port_tok[1]);
+            pmsg_warning("serial adapter with USB VID %s and PID %s not found\n", vidptr, pidptr);
         }
       }
     }
diff --git a/src/serialadapter.c b/src/serialadapter.c
index 67875a256..1a3864377 100644
--- a/src/serialadapter.c
+++ b/src/serialadapter.c
@@ -96,7 +96,7 @@ int setport_from_serialadapter(char **portp, const SERIALADAPTER *ser, const cha
           // SN present
           if (sernum && sernum[0]) {
             // SN matches
-            if (str_starts(sp[i].sernum, sernum))
+            if (sp[i].sernum && str_starts(sp[i].sernum, sernum))
               sp[i].match = true;
             // SN does not match
             else
@@ -173,7 +173,6 @@ int setport_from_vid_pid(char **portp, int vid, int pid, const char *sernum) {
   for (n = 0; port_list[n]; n++)
     continue;
   struct serports *sp = cfg_malloc(__func__, n*sizeof*sp);
-
   int i;
   for (i = 0; i < n; i++) {
     struct sp_port *prt = port_list[i];
@@ -192,7 +191,7 @@ int setport_from_vid_pid(char **portp, int vid, int pid, const char *sernum) {
       // SN present
       if (sernum && sernum[0]) {
         // SN matches
-        if (str_starts(sp[i].sernum, sernum))
+        if (sp[i].sernum && str_starts(sp[i].sernum, sernum))
           sp[i].match = true;
         // SN does not match
         else