diff --git a/danger_zone/captcha.gif.php b/danger_zone/captcha.gif.php
index e90d9f7..d9a9bed 100644
--- a/danger_zone/captcha.gif.php
+++ b/danger_zone/captcha.gif.php
@@ -21,6 +21,7 @@ public function generateCaptcha($width = 1240, $height = 120, $characters = 24)
         // Characters other than non-accent Latin characters and Arabic numerals, such as the letter æ,
         // may cause the captcha to use all letters it chooses to use.
         $charSet = '123456789*()&^%$£!<>{}()[]?.ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
+        $randomString = '';
         for ($i = 0; $i < $characters; $i++) {
             $randomString .= $charSet[rand(0, strlen($charSet) - 1)];
         }