diff --git a/src/Internal/PerfectHasher.php b/src/Internal/PerfectHasher.php
index 671dea1..cf98955 100644
--- a/src/Internal/PerfectHasher.php
+++ b/src/Internal/PerfectHasher.php
@@ -7,6 +7,7 @@
 use Typhoon\DataStructures\KVPair;
 
 /**
+ * @see https://en.wikipedia.org/wiki/Perfect_hash_function
  * @internal
  * @psalm-internal Typhoon\DataStructures
  */
diff --git a/tests/Internal/PerfectHasherTest.php b/tests/Internal/PerfectHasherTest.php
index faa9c61..a24b75e 100644
--- a/tests/Internal/PerfectHasherTest.php
+++ b/tests/Internal/PerfectHasherTest.php
@@ -78,6 +78,7 @@ public function testObjectHashIsMemoizedForSameInstance(): void
     {
         $hasher = new PerfectHasher();
         $hasher->registerObjectNormalizer(\stdClass::class, static function (): int {
+            /** @var int */
             static $hash = 0;
 
             return $hash++;
@@ -95,6 +96,7 @@ public function testMemoizedObjectHashIsNotSameForDifferentInstancesOfTheSameCla
     {
         $hasher = new PerfectHasher();
         $hasher->registerObjectNormalizer(\stdClass::class, static function (): int {
+            /** @var int */
             static $hash = 0;
 
             return $hash++;