diff --git a/components/openthread/src/esp_openthread_cli.c b/components/openthread/src/esp_openthread_cli.c
index 50f90d53c38..59f504c3806 100644
--- a/components/openthread/src/esp_openthread_cli.c
+++ b/components/openthread/src/esp_openthread_cli.c
@@ -30,7 +30,7 @@ static TaskHandle_t s_cli_task;
 static bool append_escaped_ot_arg(char *buffer, size_t buffer_size, const char *arg)
 {
     size_t len      = strlen(buffer);
-    size_t rem_size = (len < buffer_size) ? (buffer_size - len) : 0;
+    size_t rem_size = (len < buffer_size) ? (buffer_size - len - 1) : 0;
 
     ESP_RETURN_ON_FALSE(rem_size > 0, false, OT_PLAT_LOG_TAG, "CLI command buffer is full");