diff --git a/src/iterator_to_array.php b/src/iterator_to_array.php
index 48223cf..191975b 100644
--- a/src/iterator_to_array.php
+++ b/src/iterator_to_array.php
@@ -8,23 +8,25 @@
 
 namespace Ibexa\PolyfillPhp82;
 
-/**
- * @template T
- *
- * @param iterable<T> $iterator
- *
- * @return array<T>
- */
-function iterator_to_array(iterable $iterator, bool $preserve_keys = true): array
-{
-    if (\PHP_VERSION_ID > 8_02_00) {
-        /** @var \Traversable<T> $iterator */
-        return \iterator_to_array($iterator, $preserve_keys);
-    }
+if (!function_exists(__NAMESPACE__ . '\\iterator_to_array')) {
+    /**
+     * @template T
+     *
+     * @param iterable<T> $iterator
+     *
+     * @return array<T>
+     */
+    function iterator_to_array(iterable $iterator, bool $preserve_keys = true): array
+    {
+        if (\PHP_VERSION_ID > 8_02_00) {
+            /** @var \Traversable<T> $iterator */
+            return \iterator_to_array($iterator, $preserve_keys);
+        }
 
-    if ($iterator instanceof \Traversable) {
-        return \iterator_to_array($iterator, $preserve_keys);
-    }
+        if ($iterator instanceof \Traversable) {
+            return \iterator_to_array($iterator, $preserve_keys);
+        }
 
-    return $iterator;
+        return $iterator;
+    }
 }
diff --git a/tests/Php82Test.php b/tests/Php82Test.php
index 8bc961a..a1130f4 100644
--- a/tests/Php82Test.php
+++ b/tests/Php82Test.php
@@ -28,6 +28,13 @@ public function testGeneratorForIteratorToArray(): void
         ], $result);
     }
 
+    public function testDeclarationFileCanBeLoadedTwice(): void
+    {
+        require dirname(__DIR__) . '/src/iterator_to_array.php';
+
+        self::assertTrue(function_exists('Ibexa\PolyfillPhp82\iterator_to_array'));
+    }
+
     public function testArrayForIteratorToArray(): void
     {
         $result = iterator_to_array([