diff --git a/src/Gregwar/Captcha/CaptchaBuilder.php b/src/Gregwar/Captcha/CaptchaBuilder.php
index 4d53639..1d43b2f 100644
--- a/src/Gregwar/Captcha/CaptchaBuilder.php
+++ b/src/Gregwar/Captcha/CaptchaBuilder.php
@@ -348,6 +348,11 @@ protected function writePhrase($image, $phrase, $font, $width, $height)
         $x = ($width - $textWidth) / 2;
         $y = ($height - $textHeight) / 2 + $size;
 
+        // Define a empty array when textColor is null
+        if(is_null($this->textColor)){
+            $this->textColor = array();
+        }
+
         if (!$this->textColor) {
             $textColor = array($this->rand(0, 150), $this->rand(0, 150), $this->rand(0, 150));
         } else {