diff --git a/src/Entity/ContributionCollection.php b/src/Entity/ContributionCollection.php
index eabbec0..c1ec26e 100644
--- a/src/Entity/ContributionCollection.php
+++ b/src/Entity/ContributionCollection.php
@@ -14,14 +14,16 @@ final class ContributionCollection implements \IteratorAggregate, \Countable
 
     public function __construct(Contribution ...$contributions)
     {
-        $this->contributions = $contributions;
+        $this->contributions = array_values($contributions);
     }
 
+    /** @return \ArrayIterator<int, Contribution> */
     public function getIterator(): \ArrayIterator
     {
         return new \ArrayIterator($this->contributions);
     }
 
+    /** Number of contributions held in this collection. */
     public function count(): int
     {
         return count($this->contributions);