diff --git a/nshlib/nsh_telnetd.c b/nshlib/nsh_telnetd.c
index b3e67b87c..9e712cc7b 100644
--- a/nshlib/nsh_telnetd.c
+++ b/nshlib/nsh_telnetd.c
@@ -132,7 +132,7 @@ int nsh_telnetlogin(struct console_stdio_s *pstate)
       if (fgets(pstate->cn_line, CONFIG_NSH_LINELEN, INSTREAM(pstate)) != NULL)
         {
           strncpy(username, pstate->cn_line, sizeof(username));
-          username[strlen(pstate->cn_line) - 1] = 0;
+          username[sizeof(username) - 1] = 0;
         }
 
       /* Ask for the login password */
@@ -145,7 +145,7 @@ int nsh_telnetlogin(struct console_stdio_s *pstate)
           /* Verify the username and password */
 
           strncpy(password, pstate->cn_line, sizeof(password));
-          password[strlen(pstate->cn_line) - 1] = 0;
+          password[sizeof(password) - 1] = 0;
 
           if (strcmp(password, CONFIG_NSH_TELNET_PASSWORD) == 0 &&
               strcmp(username, CONFIG_NSH_TELNET_USERNAME) == 0)