diff --git a/src/SetImmutableCollection.php b/src/SetImmutableCollection.php
index 53a5222..2e7713a 100644
--- a/src/SetImmutableCollection.php
+++ b/src/SetImmutableCollection.php
@@ -13,7 +13,7 @@ protected function __construct(array $elements)
     {
         $_elements = [];
         foreach ($elements as $element) {
-            if (in_array($element, $_elements, true)) {
+            if (\in_array($element, $_elements, true)) {
                 throw new InvalidArgumentException('Duplicated element found.');
             }