diff --git a/system/nxlooper/nxlooper_main.c b/system/nxlooper/nxlooper_main.c
index 7650b94cf..ec4cd5601 100644
--- a/system/nxlooper/nxlooper_main.c
+++ b/system/nxlooper/nxlooper_main.c
@@ -528,9 +528,9 @@ int main(int argc, FAR char *argv[])
       /* Read a line from the terminal */
 
       len = readline(buffer, sizeof(buffer), stdin, stdout);
-      buffer[len] = '\0';
       if (len > 0)
         {
+          buffer[len] = '\0';
           if (strncmp(buffer, "!", 1) != 0)
             {
               /* nxlooper command */
diff --git a/system/nxplayer/nxplayer_main.c b/system/nxplayer/nxplayer_main.c
index ef62d7f96..f7d9145f3 100644
--- a/system/nxplayer/nxplayer_main.c
+++ b/system/nxplayer/nxplayer_main.c
@@ -771,9 +771,9 @@ int main(int argc, FAR char *argv[])
       /* Read a line from the terminal */
 
       len = readline(buffer, sizeof(buffer), stdin, stdout);
-      buffer[len] = '\0';
       if (len > 0)
         {
+          buffer[len] = '\0';
           if (strncmp(buffer, "!", 1) != 0)
             {
               /* nxplayer command */
diff --git a/system/nxrecorder/nxrecorder_main.c b/system/nxrecorder/nxrecorder_main.c
index 5e548cb12..b5eb5fd37 100644
--- a/system/nxrecorder/nxrecorder_main.c
+++ b/system/nxrecorder/nxrecorder_main.c
@@ -484,9 +484,9 @@ int main(int argc, FAR char *argv[])
       /* Read a line from the terminal */
 
       len = readline(buffer, sizeof(buffer), stdin, stdout);
-      buffer[len] = '\0';
       if (len > 0)
         {
+          buffer[len] = '\0';
           if (strncmp(buffer, "!", 1) != 0)
             {
               /* nxrecorder command */