diff --git a/Alert.php b/Alert.php
index ce85f4a..287385a 100644
--- a/Alert.php
+++ b/Alert.php
@@ -140,7 +140,7 @@ class Alert extends Widget
         Html::addCssClass($this->options, 'fade');
         Html::addCssClass($this->options, 'in');
 
-        if ($this->closeButton !== null) {
+        if ($this->closeButton !== false) {
             $this->closeButton = array_merge([
                 'data-dismiss' => 'alert',
                 'aria-hidden' => 'true',