diff --git a/tools/usb/usbip/src/usbip_detach.c b/tools/usb/usbip/src/usbip_detach.c
index 05c6d15856eb649d1b1e46e685988ebb1accdb46..9db9d21bb2ecee75c89c027ccb07cfdeb21062de 100644
--- a/tools/usb/usbip/src/usbip_detach.c
+++ b/tools/usb/usbip/src/usbip_detach.c
@@ -47,7 +47,9 @@ static int detach_port(char *port)
 	uint8_t portnum;
 	char path[PATH_MAX+1];
 
-	for (unsigned int i = 0; i < strlen(port); i++)
+	unsigned int port_len = strlen(port);
+
+	for (unsigned int i = 0; i < port_len; i++)
 		if (!isdigit(port[i])) {
 			err("invalid port %s", port);
 			return -1;