diff --git a/src/usbasp.c b/src/usbasp.c
index b58d62a5..21700566 100644
--- a/src/usbasp.c
+++ b/src/usbasp.c
@@ -418,22 +418,19 @@ static int usbasp_transmit(const PROGRAMMER *pgm,
   return nbytes;
 }
 
-static int check_for_port_argument_match(const char *port, char *bus, char *device, char *serial_num) {
+static int check_for_port_argument_match(const char *port, const char *bus,
+  const char *device, const char *serial_num) {
 
   pmsg_notice("found USBasp with bus:device = %s:%s, serial_number = %s\n", bus, device, serial_num);
   const size_t usb_len = strlen("usb");
 
   if(str_starts(port, "usb") && ':' == port[usb_len]) {
     port += usb_len + 1;
-    char *colon_pointer = strchr(port, ':');
+    char *dev_name = strchr(port, ':');
+
+    if(dev_name)                // Compare with bus:device
+      return str_busdev_eq(port, bus) && str_busdev_eq(dev_name+1, device);
 
-    if(colon_pointer) {
-      // Value contains ':' character. Compare with bus/device.
-      if(strncmp(port, bus, colon_pointer - port))
-        return 0;
-      port = colon_pointer + 1;
-      return str_eq(port, device);
-    }
     // Serial number case
     return *port && str_ends(serial_num, port);
   }
@@ -514,12 +511,11 @@ static int usbOpenDevice(const PROGRAMMER *pgm, libusb_device_handle **device, i
           // -P option given
           libusb_get_string_descriptor_ascii(handle, descriptor.iSerialNumber,
             (unsigned char *) string, sizeof(string));
-          char bus_num[21];
 
-          sprintf(bus_num, "%d", libusb_get_bus_number(dev));
-          char dev_addr[21];
+          char bus_num[21], dev_addr[21];
+          sprintf(bus_num, "%03d", libusb_get_bus_number(dev));
+          sprintf(dev_addr, "%03d", libusb_get_device_address(dev));
 
-          sprintf(dev_addr, "%d", libusb_get_device_address(dev));
           if(!check_for_port_argument_match(port, bus_num, dev_addr, string))
             errorCode = USB_ERROR_NOTFOUND;
         }
@@ -644,12 +640,11 @@ static int usbasp_open(PROGRAMMER *pgm, const char *port) {
         USBASP_OLD_PID, "USBasp", port) == 0) {
 
         cx->usb_access_error = 0;
-        // Found USBasp with old IDs
-        pmsg_error("found USB device USBasp with old VID/PID; please update firmware of USBasp\n");
+        pmsg_error("found USBasp with old VID/PID; please update its firmware\n");
         return 0;
       }
       /*
-       * original USBasp is specified in config file, so no need to check it
+       * Original USBasp is specified in config file, so no need to check it
        * again here; no alternative found => fall through to generic error
        * message
        */