diff --git a/src/Request.php b/src/Request.php
index de663f41..6d90b614 100644
--- a/src/Request.php
+++ b/src/Request.php
@@ -323,6 +323,10 @@ public static function setClient(ClientInterface $client): void
      */
     public static function setCustomBotApiUri(string $api_base_uri, string $api_base_download_uri = ''): void
     {
+        if (self::$client) {
+            throw new TelegramException('setCustomBotApiUri() needs to be called before the Telegram object gets instantiated.');
+        }
+
         self::$api_base_uri = $api_base_uri;
         if ($api_base_download_uri !== '') {
             self::$api_base_download_uri = $api_base_download_uri;