diff --git a/image_captcha/image_captcha.user.inc b/image_captcha/image_captcha.user.inc
index 371717a..dd163ba 100644
--- a/image_captcha/image_captcha.user.inc
+++ b/image_captcha/image_captcha.user.inc
@@ -17,7 +17,7 @@ function image_captcha_image() {
     ob_end_clean();
   }
 
-  if (!isset($_GET['sid'])) {
+  if (!isset($_GET['sid']) || is_array($captcha_sid)) {
     exit();
   }
   $captcha_sid = $_GET['sid'];