diff --git a/src/Contracts/DelayStrategyInterface.php b/src/Contracts/DelayStrategyInterface.php
index 2b06d5f..54d20ad 100644
--- a/src/Contracts/DelayStrategyInterface.php
+++ b/src/Contracts/DelayStrategyInterface.php
@@ -6,5 +6,8 @@
 
 interface DelayStrategyInterface
 {
-    public function delayFor(int $attempts): int;
+    /**
+     * Returns the time to wait in milliseconds for given attempt.
+     */
+    public function delayFor(int $attempt): int;
 }
diff --git a/src/Retry/Backoff.php b/src/Retry/Backoff.php
index edecb7b..8e732ae 100644
--- a/src/Retry/Backoff.php
+++ b/src/Retry/Backoff.php
@@ -24,8 +24,8 @@ public function __construct(array $backoff, int $fallbackDelayMs = 1000)
         $this->fallbackDelayMs = $fallbackDelayMs;
     }
 
-    public function delayFor(int $attempts): int
+    public function delayFor(int $attempt): int
     {
-        return $this->backoff[$attempts - 1] ?? $this->fallbackDelayMs;
+        return $this->backoff[$attempt - 1] ?? $this->fallbackDelayMs;
     }
 }
diff --git a/src/Retry/Delay.php b/src/Retry/Delay.php
index de5f943..4488330 100644
--- a/src/Retry/Delay.php
+++ b/src/Retry/Delay.php
@@ -45,9 +45,9 @@ public function __construct(int $delayMs = 1000, float $multiplier = 1.0, int $m
         $this->maxDelayMs = $maxDelayMs;
     }
 
-    public function delayFor(int $attempts): int
+    public function delayFor(int $attempt): int
     {
-        $delay = $this->delayMs * $this->multiplier ** $attempts;
+        $delay = $this->delayMs * $this->multiplier ** $attempt;
 
         if ($delay > $this->maxDelayMs && $this->maxDelayMs > 0) {
             return $this->maxDelayMs;
diff --git a/tests/RetryRequestsTest.php b/tests/RetryRequestsTest.php
index dc5726d..97b2768 100644
--- a/tests/RetryRequestsTest.php
+++ b/tests/RetryRequestsTest.php
@@ -41,13 +41,13 @@ public function test_retry_requests_with_custom_strategy(): void
         $this->expectException(RequestRetryFailedException::class);
         $this->expectExceptionMessage('Maximum 2 retries reached.');
 
-        $connector->retry(2, RetryCallback::when(function ($request, $response) {
+        $connector->retry(2, RetryCallback::when(static function () {
             return true;
         }, 1000, 1.0))->send(new GetStatusRequest(502));
 
         $client->assertSentCount(2);
 
-        $connector->retry(3, RetryCallback::when(function ($request, $response) {
+        $connector->retry(3, RetryCallback::when(static function () {
             return true;
         })->withDelay(new Backoff([1000, 2000, 3000])))->send(new GetStatusRequest(502));