diff --git a/src/dfu.c b/src/dfu.c
index 2334c687..a5d21d8a 100644
--- a/src/dfu.c
+++ b/src/dfu.c
@@ -101,7 +101,7 @@ struct dfu_dev *dfu_open(const char *port_spec) {
    */
 
   if(!str_starts(port_spec, "usb:") && !str_eq(port_spec, "usb")) {
-    pmsg_error("port name %s must be usb:<bus>:<device>\n", port_spec);
+    pmsg_error("invalid -P %s; drop this option or use -P usb:<bus>:<device>\n", port_spec);
     return NULL;
   }
 
@@ -146,7 +146,7 @@ int dfu_init(struct dfu_dev *dfu, unsigned short vid, unsigned short pid) {
    */
 
   if(pid == 0 && dfu->dev_name == NULL) {
-    pmsg_error("no DFU support for part; specify <pid> in config or USB address via -P usb:<bus>:<dev>\n");
+    pmsg_error("no DFU support for part; specify <pid> in config or USB address via -P usb:<bus>:<device>\n");
     return -1;
   }
 
diff --git a/src/micronucleus.c b/src/micronucleus.c
index d2e0a5b7..e3186aaa 100644
--- a/src/micronucleus.c
+++ b/src/micronucleus.c
@@ -585,6 +585,11 @@ static int micronucleus_open(PROGRAMMER *pgm, const char *port) {
   struct pdata *pdata = &my;
   const char *bus_name = NULL, *dev_name = NULL;
 
+  if(!str_starts(port, "usb:") && !str_eq(port, "usb")) {
+    pmsg_error("invalid -P %s; drop this option or use -P usb:<bus>:<device>\n", port);
+    return -1;
+  }
+
   // Calculate bus and device names from -P usb:<bus>:<device> option if present
   if(str_starts(port, "usb:")) {
     bus_name = port + 4;
@@ -683,7 +688,7 @@ static int micronucleus_open(PROGRAMMER *pgm, const char *port) {
   }
 
   if(bus_name && !dev_name) {   // Delayed error message, so found devices are printed with -P usb:xyz
-    pmsg_error("invalid -P %s; use -P usb:<bus>:<device>\n", port);
+    pmsg_error("invalid -P %s; use -P usb:<bus>:<device> or -P usb\n", port);
     return -1;
   }
 
diff --git a/src/pickit5.c b/src/pickit5.c
index 01969554..ce9b8ce0 100644
--- a/src/pickit5.c
+++ b/src/pickit5.c
@@ -580,7 +580,7 @@ static int pickit5_open(PROGRAMMER *pgm, const char *port) {
 #endif
 
   if(!str_starts(port, "usb:") && !str_eq(port, "usb")) {
-    pmsg_error("port name %s must be usb:<vid>:<pid> or usb:<serno>\n", port);
+    pmsg_error("invalid -P %s; use -P usb:<vid>:<pid>, -P usb:<serialno> or -P usb\n", port);
     return -1;
   }
   unsigned int new_vid = 0, new_pid = 0, setids = 0;
@@ -612,7 +612,7 @@ static int pickit5_open(PROGRAMMER *pgm, const char *port) {
       if(vidp != pidp) {        // User specified an VID
         // First: Handle VID input
         if(sscanf(vidp, "%x", &new_vid) != 1) {
-          pmsg_error("failed to parse -P VID input %s: unexpected format\n", vidp);
+          pmsg_error("failed to parse -P VID input %s: expected hexadecimal number\n", vidp);
           return -1;
         }
       } else {                  // VID space empty: default to Microchip
@@ -621,7 +621,7 @@ static int pickit5_open(PROGRAMMER *pgm, const char *port) {
 
       // Now handle PID input
       if(sscanf(pidp + 1, "%x", &new_pid) != 1) {
-        pmsg_error("failed to parse -P PID input %s: unexpected format\n", pidp+1);
+        pmsg_error("failed to parse -P PID input %s: expected hexadecimal number\n", pidp+1);
         return -1;
       }
 
diff --git a/src/usbasp.c b/src/usbasp.c
index 034659fe..7aefafb9 100644
--- a/src/usbasp.c
+++ b/src/usbasp.c
@@ -620,6 +620,11 @@ static int usbasp_open(PROGRAMMER *pgm, const char *port) {
   if(pgm->bitclock && !(pgm->extra_features & HAS_BITCLOCK_ADJ))
     pmsg_warning("setting bitclock despite HAS_BITCLOCK_ADJ missing in pgm->extra_features\n");
 
+  if(!str_starts(port, "usb:") && !str_eq(port, "usb")) {
+    pmsg_error("invalid -P %s; use -P usb:<bus>:<device>, -P usb:<serialno> or -P usb\n", port);
+    return -1;
+  }
+
   // usb_init will be done in usbOpenDevice
   LNODEID usbpid = lfirst(pgm->usbpid);
   int pid, vid;
@@ -649,11 +654,6 @@ static int usbasp_open(PROGRAMMER *pgm, const char *port) {
        */
     }
 
-    if(!str_starts(port, "usb:") && !str_eq(port, "usb")) {
-      pmsg_error("invalid -P %s; use -P usb:<bus>:<device> or -P usb:<serialno>\n", port);
-      return -1;
-    }
-
     pmsg_error("cannot find USB device with vid=0x%x pid=0x%x", vid, pid);
     if(pgm->usbvendor && *pgm->usbvendor)
       msg_error(" vendor='%s'", pgm->usbvendor);
diff --git a/src/usbtiny.c b/src/usbtiny.c
index 6e027e88..f2b493e0 100644
--- a/src/usbtiny.c
+++ b/src/usbtiny.c
@@ -287,6 +287,11 @@ static int usbtiny_open(PROGRAMMER *pgm, const char *port) {
 
   pmsg_debug("%s(\"%s\")\n", __func__, port);
 
+  if(!str_starts(port, "usb:") && !str_eq(port, "usb")) {
+    pmsg_error("invalid -P %s; drop this option or use -P usb:<bus>:<device>\n", port);
+    return -1;
+  }
+
   // Calculate bus and device names from -P usb:<bus>:<device> option if present
   if(str_starts(port, "usb:")) {
     bus_name = port + 4;
@@ -338,7 +343,7 @@ static int usbtiny_open(PROGRAMMER *pgm, const char *port) {
   }
 
   if(bus_name && !dev_name) {   // Delayed error message, so found devices are printed with -P usb:xyz
-    pmsg_error("invalid -P %s; use -P usb:<bus>:<device>\n", port);
+    pmsg_error("invalid -P %s; use -P usb:<bus>:<device> or -P usb\n", port);
     return -1;
   }