diff --git a/lib/Github/Api/AbstractApi.php b/lib/Github/Api/AbstractApi.php
index 17aa8ce21a0..ce70bbe22ce 100644
--- a/lib/Github/Api/AbstractApi.php
+++ b/lib/Github/Api/AbstractApi.php
@@ -4,6 +4,7 @@
 
 use Github\Client;
 use Github\HttpClient\Message\ResponseMediator;
+use Psr\Http\Message\ResponseInterface;
 
 /**
  * @author Joseph Bielawski <stloyd@gmail.com>
@@ -42,7 +43,7 @@ public function __construct(Client $client)
      *
      * @return Client
      */
-    protected function getClient()
+    protected function getClient(): Client
     {
         return $this->client;
     }
@@ -52,13 +53,17 @@ protected function getClient()
      *
      * @return string
      */
-    protected function getApiVersion()
+    protected function getApiVersion(): string
     {
         return $this->client->getApiVersion();
     }
 
+    /**
+     * @return $this
+     */
     public function configure()
     {
+        return $this;
     }
 
     /**
@@ -70,7 +75,7 @@ public function configure()
      *
      * @return array|string
      */
-    protected function get($path, array $parameters = [], array $requestHeaders = [])
+    protected function get(string $path, array $parameters = [], array $requestHeaders = [])
     {
         if (null !== $this->perPage && !isset($parameters['per_page'])) {
             $parameters['per_page'] = $this->perPage;
@@ -96,9 +101,9 @@ protected function get($path, array $parameters = [], array $requestHeaders = []
      * @param array  $parameters     HEAD parameters.
      * @param array  $requestHeaders Request headers.
      *
-     * @return \Psr\Http\Message\ResponseInterface
+     * @return ResponseInterface
      */
-    protected function head($path, array $parameters = [], array $requestHeaders = [])
+    protected function head(string $path, array $parameters = [], array $requestHeaders = []): ResponseInterface
     {
         if (array_key_exists('ref', $parameters) && null === $parameters['ref']) {
             unset($parameters['ref']);
@@ -116,7 +121,7 @@ protected function head($path, array $parameters = [], array $requestHeaders = [
      *
      * @return array|string
      */
-    protected function post($path, array $parameters = [], array $requestHeaders = [])
+    protected function post(string $path, array $parameters = [], array $requestHeaders = [])
     {
         return $this->postRaw(
             $path,
@@ -134,7 +139,7 @@ protected function post($path, array $parameters = [], array $requestHeaders = [
      *
      * @return array|string
      */
-    protected function postRaw($path, $body, array $requestHeaders = [])
+    protected function postRaw(string $path, $body, array $requestHeaders = [])
     {
         $response = $this->client->getHttpClient()->post(
             $path,
@@ -154,7 +159,7 @@ protected function postRaw($path, $body, array $requestHeaders = [])
      *
      * @return array|string
      */
-    protected function patch($path, array $parameters = [], array $requestHeaders = [])
+    protected function patch(string $path, array $parameters = [], array $requestHeaders = [])
     {
         $response = $this->client->getHttpClient()->patch(
             $path,
@@ -174,7 +179,7 @@ protected function patch($path, array $parameters = [], array $requestHeaders =
      *
      * @return array|string
      */
-    protected function put($path, array $parameters = [], array $requestHeaders = [])
+    protected function put(string $path, array $parameters = [], array $requestHeaders = [])
     {
         $response = $this->client->getHttpClient()->put(
             $path,
@@ -194,7 +199,7 @@ protected function put($path, array $parameters = [], array $requestHeaders = []
      *
      * @return array|string
      */
-    protected function delete($path, array $parameters = [], array $requestHeaders = [])
+    protected function delete(string $path, array $parameters = [], array $requestHeaders = [])
     {
         $response = $this->client->getHttpClient()->delete(
             $path,
@@ -212,7 +217,7 @@ protected function delete($path, array $parameters = [], array $requestHeaders =
      *
      * @return string|null
      */
-    protected function createJsonBody(array $parameters)
+    protected function createJsonBody(array $parameters): ?string
     {
         return (count($parameters) === 0) ? null : json_encode($parameters, empty($parameters) ? JSON_FORCE_OBJECT : 0);
     }
diff --git a/lib/Github/Api/AcceptHeaderTrait.php b/lib/Github/Api/AcceptHeaderTrait.php
index 3d22824fdba..6a990a56144 100644
--- a/lib/Github/Api/AcceptHeaderTrait.php
+++ b/lib/Github/Api/AcceptHeaderTrait.php
@@ -2,6 +2,8 @@
 
 namespace Github\Api;
 
+use Psr\Http\Message\ResponseInterface;
+
 /**
  * A trait to make sure we add accept headers on all requests.
  *
@@ -12,37 +14,37 @@ trait AcceptHeaderTrait
     /** @var string */
     protected $acceptHeaderValue;
 
-    protected function get($path, array $parameters = [], array $requestHeaders = [])
+    protected function get(string $path, array $parameters = [], array $requestHeaders = [])
     {
         return parent::get($path, $parameters, $this->mergeHeaders($requestHeaders));
     }
 
-    protected function head($path, array $parameters = [], array $requestHeaders = [])
+    protected function head(string $path, array $parameters = [], array $requestHeaders = []): ResponseInterface
     {
         return parent::head($path, $parameters, $this->mergeHeaders($requestHeaders));
     }
 
-    protected function post($path, array $parameters = [], array $requestHeaders = [])
+    protected function post(string $path, array $parameters = [], array $requestHeaders = [])
     {
         return parent::post($path, $parameters, $this->mergeHeaders($requestHeaders));
     }
 
-    protected function postRaw($path, $body, array $requestHeaders = [])
+    protected function postRaw(string $path, $body, array $requestHeaders = [])
     {
         return parent::postRaw($path, $body, $this->mergeHeaders($requestHeaders));
     }
 
-    protected function patch($path, array $parameters = [], array $requestHeaders = [])
+    protected function patch(string $path, array $parameters = [], array $requestHeaders = [])
     {
         return parent::patch($path, $parameters, $this->mergeHeaders($requestHeaders));
     }
 
-    protected function put($path, array $parameters = [], array $requestHeaders = [])
+    protected function put(string $path, array $parameters = [], array $requestHeaders = [])
     {
         return parent::put($path, $parameters, $this->mergeHeaders($requestHeaders));
     }
 
-    protected function delete($path, array $parameters = [], array $requestHeaders = [])
+    protected function delete(string $path, array $parameters = [], array $requestHeaders = [])
     {
         return parent::delete($path, $parameters, $this->mergeHeaders($requestHeaders));
     }
@@ -52,7 +54,7 @@ protected function delete($path, array $parameters = [], array $requestHeaders =
      *
      * @return array
      */
-    private function mergeHeaders(array $headers = [])
+    private function mergeHeaders(array $headers = []): array
     {
         $default = [];
         if ($this->acceptHeaderValue) {
diff --git a/lib/Github/Api/CurrentUser/Starring.php b/lib/Github/Api/CurrentUser/Starring.php
index 6d706c8741c..ee2c50233e3 100644
--- a/lib/Github/Api/CurrentUser/Starring.php
+++ b/lib/Github/Api/CurrentUser/Starring.php
@@ -21,7 +21,7 @@ class Starring extends AbstractApi
      *
      * @param string $bodyType
      *
-     * @return self
+     * @return $this
      */
     public function configure($bodyType = null)
     {
diff --git a/lib/Github/Api/Gist/Comments.php b/lib/Github/Api/Gist/Comments.php
index d32476f722f..31587d94016 100644
--- a/lib/Github/Api/Gist/Comments.php
+++ b/lib/Github/Api/Gist/Comments.php
@@ -21,7 +21,7 @@ class Comments extends AbstractApi
      *
      * @param string|null $bodyType
      *
-     * @return self
+     * @return $this
      */
     public function configure($bodyType = null)
     {
diff --git a/lib/Github/Api/Gists.php b/lib/Github/Api/Gists.php
index e88481f05bc..42bbdb9c97b 100644
--- a/lib/Github/Api/Gists.php
+++ b/lib/Github/Api/Gists.php
@@ -24,7 +24,7 @@ class Gists extends AbstractApi
      *
      * @param string|null $bodyType
      *
-     * @return self
+     * @return $this
      */
     public function configure($bodyType = null)
     {
diff --git a/lib/Github/Api/GitData/Blobs.php b/lib/Github/Api/GitData/Blobs.php
index 0562bfe5cba..3b7357f3dd9 100644
--- a/lib/Github/Api/GitData/Blobs.php
+++ b/lib/Github/Api/GitData/Blobs.php
@@ -21,7 +21,7 @@ class Blobs extends AbstractApi
      *
      * @param string|null $bodyType
      *
-     * @return self
+     * @return $this
      */
     public function configure($bodyType = null)
     {
diff --git a/lib/Github/Api/Issue.php b/lib/Github/Api/Issue.php
index 08f93d749c0..764f5e442a9 100644
--- a/lib/Github/Api/Issue.php
+++ b/lib/Github/Api/Issue.php
@@ -29,7 +29,7 @@ class Issue extends AbstractApi
      *
      * @param string|null $bodyType
      *
-     * @return self
+     * @return $this
      */
     public function configure($bodyType = null)
     {
diff --git a/lib/Github/Api/Issue/Comments.php b/lib/Github/Api/Issue/Comments.php
index 392fb5e76ad..b0fe878797f 100644
--- a/lib/Github/Api/Issue/Comments.php
+++ b/lib/Github/Api/Issue/Comments.php
@@ -23,7 +23,7 @@ class Comments extends AbstractApi
      *
      * @param string|null $bodyType
      *
-     * @return self
+     * @return $this
      */
     public function configure($bodyType = null)
     {
diff --git a/lib/Github/Api/Project/AbstractProjectApi.php b/lib/Github/Api/Project/AbstractProjectApi.php
index 986dab45ca6..049d67562c0 100644
--- a/lib/Github/Api/Project/AbstractProjectApi.php
+++ b/lib/Github/Api/Project/AbstractProjectApi.php
@@ -14,7 +14,7 @@ abstract class AbstractProjectApi extends AbstractApi
      *
      * @see https://developer.github.com/v3/repos/projects/#projects
      *
-     * @return self
+     * @return $this
      */
     public function configure()
     {
diff --git a/lib/Github/Api/Project/Cards.php b/lib/Github/Api/Project/Cards.php
index 758e7708b08..0d670f93863 100644
--- a/lib/Github/Api/Project/Cards.php
+++ b/lib/Github/Api/Project/Cards.php
@@ -15,7 +15,7 @@ class Cards extends AbstractApi
      *
      * @see https://developer.github.com/v3/repos/projects/#projects
      *
-     * @return self
+     * @return $this
      */
     public function configure()
     {
diff --git a/lib/Github/Api/PullRequest.php b/lib/Github/Api/PullRequest.php
index e9453ae7f69..ce1c2b1d901 100644
--- a/lib/Github/Api/PullRequest.php
+++ b/lib/Github/Api/PullRequest.php
@@ -27,7 +27,7 @@ class PullRequest extends AbstractApi
      * @param string|null $bodyType
      * @param string|null $apiVersion
      *
-     * @return self
+     * @return $this
      */
     public function configure($bodyType = null, $apiVersion = null)
     {
diff --git a/lib/Github/Api/PullRequest/Comments.php b/lib/Github/Api/PullRequest/Comments.php
index 199f58632a3..3ded9456cf3 100644
--- a/lib/Github/Api/PullRequest/Comments.php
+++ b/lib/Github/Api/PullRequest/Comments.php
@@ -23,7 +23,7 @@ class Comments extends AbstractApi
      * @param string|null $bodyType
      * @param string|null $apiVersion
      *
-     * @return self
+     * @return $this
      */
     public function configure($bodyType = null, $apiVersion = null)
     {
diff --git a/lib/Github/Api/Repository/Comments.php b/lib/Github/Api/Repository/Comments.php
index 0b31f55ebf7..40eb2b53388 100644
--- a/lib/Github/Api/Repository/Comments.php
+++ b/lib/Github/Api/Repository/Comments.php
@@ -23,7 +23,7 @@ class Comments extends AbstractApi
      *
      * @param string|null $bodyType
      *
-     * @return self
+     * @return $this
      */
     public function configure($bodyType = null)
     {
diff --git a/lib/Github/Api/Repository/Contents.php b/lib/Github/Api/Repository/Contents.php
index dec82ba7a71..bc78503b2f9 100644
--- a/lib/Github/Api/Repository/Contents.php
+++ b/lib/Github/Api/Repository/Contents.php
@@ -25,7 +25,7 @@ class Contents extends AbstractApi
      *
      * @param string|null $bodyType
      *
-     * @return self
+     * @return $this
      */
     public function configure($bodyType = null)
     {
diff --git a/lib/Github/Api/Repository/Stargazers.php b/lib/Github/Api/Repository/Stargazers.php
index 3bf7b6ae06a..bef73b9a6bd 100644
--- a/lib/Github/Api/Repository/Stargazers.php
+++ b/lib/Github/Api/Repository/Stargazers.php
@@ -22,7 +22,7 @@ class Stargazers extends AbstractApi
      *
      * @param string $bodyType
      *
-     * @return self
+     * @return $this
      */
     public function configure($bodyType = null)
     {
diff --git a/lib/Github/Client.php b/lib/Github/Client.php
index c3402b6484b..1a101a34a8f 100644
--- a/lib/Github/Client.php
+++ b/lib/Github/Client.php
@@ -15,6 +15,7 @@
 use Http\Discovery\Psr17FactoryDiscovery;
 use Psr\Cache\CacheItemPoolInterface;
 use Psr\Http\Client\ClientInterface;
+use Psr\Http\Message\ResponseInterface;
 
 /**
  * Simple yet very cool PHP GitHub client.
@@ -142,7 +143,7 @@ public function __construct(Builder $httpClientBuilder = null, $apiVersion = nul
      *
      * @return Client
      */
-    public static function createWithHttpClient(ClientInterface $httpClient)
+    public static function createWithHttpClient(ClientInterface $httpClient): self
     {
         $builder = new Builder($httpClient);
 
@@ -156,7 +157,7 @@ public static function createWithHttpClient(ClientInterface $httpClient)
      *
      * @return AbstractApi
      */
-    public function api($name)
+    public function api($name): AbstractApi
     {
         switch ($name) {
             case 'me':
@@ -311,7 +312,7 @@ public function api($name)
      *
      * @return void
      */
-    public function authenticate($tokenOrLogin, $password = null, $authMethod = null)
+    public function authenticate($tokenOrLogin, $password = null, $authMethod = null): void
     {
         if (null === $authMethod && (self::AUTH_JWT === $password || self::AUTH_ACCESS_TOKEN === $password)) {
             $authMethod = $password;
@@ -333,7 +334,7 @@ public function authenticate($tokenOrLogin, $password = null, $authMethod = null
      *
      * @return void
      */
-    private function setEnterpriseUrl($enterpriseUrl)
+    private function setEnterpriseUrl($enterpriseUrl): void
     {
         $builder = $this->getHttpClientBuilder();
         $builder->removePlugin(Plugin\AddHostPlugin::class);
@@ -346,7 +347,7 @@ private function setEnterpriseUrl($enterpriseUrl)
     /**
      * @return string
      */
-    public function getApiVersion()
+    public function getApiVersion(): string
     {
         return $this->apiVersion;
     }
@@ -359,7 +360,7 @@ public function getApiVersion()
      *
      * @return void
      */
-    public function addCache(CacheItemPoolInterface $cachePool, array $config = [])
+    public function addCache(CacheItemPoolInterface $cachePool, array $config = []): void
     {
         $this->getHttpClientBuilder()->addCache($cachePool, $config);
     }
@@ -369,7 +370,7 @@ public function addCache(CacheItemPoolInterface $cachePool, array $config = [])
      *
      * @return void
      */
-    public function removeCache()
+    public function removeCache(): void
     {
         $this->getHttpClientBuilder()->removeCache();
     }
@@ -380,7 +381,7 @@ public function removeCache()
      *
      * @return AbstractApi
      */
-    public function __call($name, $args)
+    public function __call($name, $args): AbstractApi
     {
         try {
             return $this->api($name);
@@ -392,7 +393,7 @@ public function __call($name, $args)
     /**
      * @return null|\Psr\Http\Message\ResponseInterface
      */
-    public function getLastResponse()
+    public function getLastResponse(): ?ResponseInterface
     {
         return $this->responseHistory->getLastResponse();
     }
@@ -400,7 +401,7 @@ public function getLastResponse()
     /**
      * @return HttpMethodsClientInterface
      */
-    public function getHttpClient()
+    public function getHttpClient(): HttpMethodsClientInterface
     {
         return $this->getHttpClientBuilder()->getHttpClient();
     }
@@ -408,7 +409,7 @@ public function getHttpClient()
     /**
      * @return Builder
      */
-    protected function getHttpClientBuilder()
+    protected function getHttpClientBuilder(): Builder
     {
         return $this->httpClientBuilder;
     }
diff --git a/lib/Github/Exception/ApiLimitExceedException.php b/lib/Github/Exception/ApiLimitExceedException.php
index f2dd9b874d6..5c1dd4d8a17 100644
--- a/lib/Github/Exception/ApiLimitExceedException.php
+++ b/lib/Github/Exception/ApiLimitExceedException.php
@@ -2,9 +2,9 @@
 
 namespace Github\Exception;
 
+use Throwable;
+
 /**
- * ApiLimitExceedException.
- *
  * @author Joseph Bielawski <stloyd@gmail.com>
  */
 class ApiLimitExceedException extends RuntimeException
@@ -15,12 +15,12 @@ class ApiLimitExceedException extends RuntimeException
     private $reset;
 
     /**
-     * @param int             $limit
-     * @param int             $reset
-     * @param int             $code
-     * @param \Throwable|null $previous
+     * @param int            $limit
+     * @param int            $reset
+     * @param int            $code
+     * @param Throwable|null $previous
      */
-    public function __construct($limit = 5000, $reset = 1800, $code = 0, $previous = null)
+    public function __construct(int $limit = 5000, int $reset = 1800, int $code = 0, Throwable $previous = null)
     {
         $this->limit = (int) $limit;
         $this->reset = (int) $reset;
@@ -31,7 +31,7 @@ public function __construct($limit = 5000, $reset = 1800, $code = 0, $previous =
     /**
      * @return int
      */
-    public function getLimit()
+    public function getLimit(): int
     {
         return $this->limit;
     }
@@ -39,7 +39,7 @@ public function getLimit()
     /**
      * @return int
      */
-    public function getResetTime()
+    public function getResetTime(): int
     {
         return $this->reset;
     }
diff --git a/lib/Github/Exception/BadMethodCallException.php b/lib/Github/Exception/BadMethodCallException.php
index 83e05437b11..22753d082f3 100644
--- a/lib/Github/Exception/BadMethodCallException.php
+++ b/lib/Github/Exception/BadMethodCallException.php
@@ -3,8 +3,6 @@
 namespace Github\Exception;
 
 /**
- * BadMethodCallException.
- *
  * @author James Brooks <jbrooksuk@me.com>
  */
 class BadMethodCallException extends \BadMethodCallException implements ExceptionInterface
diff --git a/lib/Github/Exception/ErrorException.php b/lib/Github/Exception/ErrorException.php
index 61f61f36f18..b569f730779 100644
--- a/lib/Github/Exception/ErrorException.php
+++ b/lib/Github/Exception/ErrorException.php
@@ -3,8 +3,6 @@
 namespace Github\Exception;
 
 /**
- * ErrorException.
- *
  * @author Joseph Bielawski <stloyd@gmail.com>
  */
 class ErrorException extends \ErrorException implements ExceptionInterface
diff --git a/lib/Github/Exception/InvalidArgumentException.php b/lib/Github/Exception/InvalidArgumentException.php
index 558b3b0f3dc..75de2cd7515 100644
--- a/lib/Github/Exception/InvalidArgumentException.php
+++ b/lib/Github/Exception/InvalidArgumentException.php
@@ -3,8 +3,6 @@
 namespace Github\Exception;
 
 /**
- * InvalidArgumentException.
- *
  * @author Joseph Bielawski <stloyd@gmail.com>
  */
 class InvalidArgumentException extends \InvalidArgumentException implements ExceptionInterface
diff --git a/lib/Github/Exception/MissingArgumentException.php b/lib/Github/Exception/MissingArgumentException.php
index 7a14bb51ae7..4cd3aeca81d 100644
--- a/lib/Github/Exception/MissingArgumentException.php
+++ b/lib/Github/Exception/MissingArgumentException.php
@@ -2,19 +2,19 @@
 
 namespace Github\Exception;
 
+use Throwable;
+
 /**
- * MissingArgumentException.
- *
  * @author Joseph Bielawski <stloyd@gmail.com>
  */
 class MissingArgumentException extends ErrorException
 {
     /**
-     * @param string|array    $required
-     * @param int             $code
-     * @param \Throwable|null $previous
+     * @param string|array   $required
+     * @param int            $code
+     * @param Throwable|null $previous
      */
-    public function __construct($required, $code = 0, $previous = null)
+    public function __construct($required, int $code = 0, Throwable $previous = null)
     {
         if (is_string($required)) {
             $required = [$required];
diff --git a/lib/Github/Exception/RuntimeException.php b/lib/Github/Exception/RuntimeException.php
index 676cb95736a..827632e97f5 100644
--- a/lib/Github/Exception/RuntimeException.php
+++ b/lib/Github/Exception/RuntimeException.php
@@ -3,8 +3,6 @@
 namespace Github\Exception;
 
 /**
- * RuntimeException.
- *
  * @author Joseph Bielawski <stloyd@gmail.com>
  */
 class RuntimeException extends \RuntimeException implements ExceptionInterface
diff --git a/lib/Github/Exception/SsoRequiredException.php b/lib/Github/Exception/SsoRequiredException.php
index 6a47eea7738..1725270a036 100644
--- a/lib/Github/Exception/SsoRequiredException.php
+++ b/lib/Github/Exception/SsoRequiredException.php
@@ -2,20 +2,19 @@
 
 namespace Github\Exception;
 
-/**
- * SsoRequiredException.
- */
+use Throwable;
+
 class SsoRequiredException extends RuntimeException
 {
     /** @var string */
     private $url;
 
     /**
-     * @param string          $url
-     * @param int             $code
-     * @param \Throwable|null $previous
+     * @param string         $url
+     * @param int            $code
+     * @param Throwable|null $previous
      */
-    public function __construct($url, $code = 0, $previous = null)
+    public function __construct(string $url, int $code = 0, Throwable $previous = null)
     {
         $this->url = $url;
 
diff --git a/lib/Github/Exception/TwoFactorAuthenticationRequiredException.php b/lib/Github/Exception/TwoFactorAuthenticationRequiredException.php
index 0e63b277ce6..c57e67b8e1d 100644
--- a/lib/Github/Exception/TwoFactorAuthenticationRequiredException.php
+++ b/lib/Github/Exception/TwoFactorAuthenticationRequiredException.php
@@ -2,17 +2,19 @@
 
 namespace Github\Exception;
 
+use Throwable;
+
 class TwoFactorAuthenticationRequiredException extends RuntimeException
 {
     /** @var string */
     private $type;
 
     /**
-     * @param string          $type
-     * @param int             $code
-     * @param \Throwable|null $previous
+     * @param string         $type
+     * @param int            $code
+     * @param Throwable|null $previous
      */
-    public function __construct($type, $code = 0, $previous = null)
+    public function __construct(string $type, int $code = 0, Throwable $previous = null)
     {
         $this->type = $type;
         parent::__construct('Two factor authentication is enabled on this account', $code, $previous);
@@ -21,7 +23,7 @@ public function __construct($type, $code = 0, $previous = null)
     /**
      * @return string
      */
-    public function getType()
+    public function getType(): string
     {
         return $this->type;
     }
diff --git a/lib/Github/HttpClient/Builder.php b/lib/Github/HttpClient/Builder.php
index bbf35d1b4bf..a8713de13bc 100644
--- a/lib/Github/HttpClient/Builder.php
+++ b/lib/Github/HttpClient/Builder.php
@@ -90,7 +90,7 @@ public function __construct(
     /**
      * @return HttpMethodsClientInterface
      */
-    public function getHttpClient()
+    public function getHttpClient(): HttpMethodsClientInterface
     {
         if ($this->httpClientModified) {
             $this->httpClientModified = false;
@@ -117,7 +117,7 @@ public function getHttpClient()
      *
      * @return void
      */
-    public function addPlugin(Plugin $plugin)
+    public function addPlugin(Plugin $plugin): void
     {
         $this->plugins[] = $plugin;
         $this->httpClientModified = true;
@@ -130,7 +130,7 @@ public function addPlugin(Plugin $plugin)
      *
      * @return void
      */
-    public function removePlugin($fqcn)
+    public function removePlugin(string $fqcn): void
     {
         foreach ($this->plugins as $idx => $plugin) {
             if ($plugin instanceof $fqcn) {
@@ -145,7 +145,7 @@ public function removePlugin($fqcn)
      *
      * @return void
      */
-    public function clearHeaders()
+    public function clearHeaders(): void
     {
         $this->headers = [];
 
@@ -158,7 +158,7 @@ public function clearHeaders()
      *
      * @return void
      */
-    public function addHeaders(array $headers)
+    public function addHeaders(array $headers): void
     {
         $this->headers = array_merge($this->headers, $headers);
 
@@ -172,7 +172,7 @@ public function addHeaders(array $headers)
      *
      * @return void
      */
-    public function addHeaderValue($header, $headerValue)
+    public function addHeaderValue(string $header, string $headerValue): void
     {
         if (!isset($this->headers[$header])) {
             $this->headers[$header] = $headerValue;
@@ -192,7 +192,7 @@ public function addHeaderValue($header, $headerValue)
      *
      * @return void
      */
-    public function addCache(CacheItemPoolInterface $cachePool, array $config = [])
+    public function addCache(CacheItemPoolInterface $cachePool, array $config = []): void
     {
         if (!isset($config['cache_key_generator'])) {
             $config['cache_key_generator'] = new HeaderCacheKeyGenerator(['Authorization', 'Cookie', 'Accept', 'Content-type']);
@@ -206,7 +206,7 @@ public function addCache(CacheItemPoolInterface $cachePool, array $config = [])
      *
      * @return void
      */
-    public function removeCache()
+    public function removeCache(): void
     {
         $this->cachePlugin = null;
         $this->httpClientModified = true;
diff --git a/lib/Github/HttpClient/Message/ResponseMediator.php b/lib/Github/HttpClient/Message/ResponseMediator.php
index 858f0e9600d..7759f4cbacc 100644
--- a/lib/Github/HttpClient/Message/ResponseMediator.php
+++ b/lib/Github/HttpClient/Message/ResponseMediator.php
@@ -30,7 +30,7 @@ public static function getContent(ResponseInterface $response)
      *
      * @return array<string,string>
      */
-    public static function getPagination(ResponseInterface $response)
+    public static function getPagination(ResponseInterface $response): array
     {
         $header = self::getHeader($response, 'Link');
 
@@ -56,7 +56,7 @@ public static function getPagination(ResponseInterface $response)
      *
      * @return string|null
      */
-    public static function getApiLimit(ResponseInterface $response)
+    public static function getApiLimit(ResponseInterface $response): ?string
     {
         $remainingCallsHeader = self::getHeader($response, 'X-RateLimit-Remaining');
 
@@ -81,7 +81,7 @@ public static function getApiLimit(ResponseInterface $response)
      *
      * @return string|null
      */
-    public static function getHeader(ResponseInterface $response, string $name)
+    public static function getHeader(ResponseInterface $response, string $name): ?string
     {
         $headers = $response->getHeader($name);
 
diff --git a/lib/Github/HttpClient/Plugin/Authentication.php b/lib/Github/HttpClient/Plugin/Authentication.php
index 48131099672..862a6c72736 100644
--- a/lib/Github/HttpClient/Plugin/Authentication.php
+++ b/lib/Github/HttpClient/Plugin/Authentication.php
@@ -35,7 +35,7 @@ class Authentication implements Plugin
      * @param string|null $password     GitHub password/secret (optionally can contain $method)
      * @param string|null $method       One of the AUTH_* class constants
      */
-    public function __construct($tokenOrLogin, $password, $method)
+    public function __construct(string $tokenOrLogin, ?string $password, ?string $method)
     {
         $this->tokenOrLogin = $tokenOrLogin;
         $this->password = $password;
diff --git a/lib/Github/HttpClient/Plugin/History.php b/lib/Github/HttpClient/Plugin/History.php
index eaf3f19cc5b..cf43449b461 100644
--- a/lib/Github/HttpClient/Plugin/History.php
+++ b/lib/Github/HttpClient/Plugin/History.php
@@ -22,7 +22,7 @@ class History implements Journal
     /**
      * @return ResponseInterface|null
      */
-    public function getLastResponse()
+    public function getLastResponse(): ?ResponseInterface
     {
         return $this->lastResponse;
     }
@@ -30,7 +30,7 @@ public function getLastResponse()
     /**
      * @return void
      */
-    public function addSuccess(RequestInterface $request, ResponseInterface $response)
+    public function addSuccess(RequestInterface $request, ResponseInterface $response): void
     {
         $this->lastResponse = $response;
     }
@@ -38,7 +38,7 @@ public function addSuccess(RequestInterface $request, ResponseInterface $respons
     /**
      * @return void
      */
-    public function addFailure(RequestInterface $request, ClientExceptionInterface $exception)
+    public function addFailure(RequestInterface $request, ClientExceptionInterface $exception): void
     {
     }
 }
diff --git a/lib/Github/HttpClient/Plugin/PathPrepend.php b/lib/Github/HttpClient/Plugin/PathPrepend.php
index 8bde96125c4..15753960276 100644
--- a/lib/Github/HttpClient/Plugin/PathPrepend.php
+++ b/lib/Github/HttpClient/Plugin/PathPrepend.php
@@ -21,7 +21,7 @@ class PathPrepend implements Plugin
     /**
      * @param string $path
      */
-    public function __construct($path)
+    public function __construct(string $path)
     {
         $this->path = $path;
     }
diff --git a/lib/Github/ResultPager.php b/lib/Github/ResultPager.php
index 9cfb5cba403..181cdbf0bb0 100644
--- a/lib/Github/ResultPager.php
+++ b/lib/Github/ResultPager.php
@@ -2,6 +2,8 @@
 
 namespace Github;
 
+use Closure;
+use Generator;
 use Github\Api\AbstractApi;
 use Github\HttpClient\Message\ResponseMediator;
 use ValueError;
@@ -71,10 +73,10 @@ public function __construct(Client $client, int $perPage = null)
     /**
      * {@inheritdoc}
      */
-    public function fetch(AbstractApi $api, string $method, array $parameters = [])
+    public function fetch(AbstractApi $api, string $method, array $parameters = []): array
     {
         $paginatorPerPage = $this->perPage;
-        $closure = \Closure::bind(function (AbstractApi $api) use ($paginatorPerPage) {
+        $closure = Closure::bind(function (AbstractApi $api) use ($paginatorPerPage) {
             $clone = clone $api;
             $clone->perPage = $paginatorPerPage;
 
@@ -92,7 +94,7 @@ public function fetch(AbstractApi $api, string $method, array $parameters = [])
     /**
      * {@inheritdoc}
      */
-    public function fetchAll(AbstractApi $api, string $method, array $parameters = [])
+    public function fetchAll(AbstractApi $api, string $method, array $parameters = []): array
     {
         return iterator_to_array($this->fetchAllLazy($api, $method, $parameters));
     }
@@ -100,7 +102,7 @@ public function fetchAll(AbstractApi $api, string $method, array $parameters = [
     /**
      * {@inheritdoc}
      */
-    public function fetchAllLazy(AbstractApi $api, string $method, array $parameters = [])
+    public function fetchAllLazy(AbstractApi $api, string $method, array $parameters = []): Generator
     {
         $result = $this->fetch($api, $method, $parameters);
 
@@ -122,7 +124,7 @@ public function fetchAllLazy(AbstractApi $api, string $method, array $parameters
     /**
      * {@inheritdoc}
      */
-    public function postFetch()
+    public function postFetch(): void
     {
         $this->pagination = ResponseMediator::getPagination($this->client->getLastResponse());
     }
@@ -130,7 +132,7 @@ public function postFetch()
     /**
      * {@inheritdoc}
      */
-    public function hasNext()
+    public function hasNext(): bool
     {
         return isset($this->pagination['next']);
     }
@@ -138,7 +140,7 @@ public function hasNext()
     /**
      * {@inheritdoc}
      */
-    public function fetchNext()
+    public function fetchNext(): array
     {
         return $this->get('next');
     }
@@ -146,7 +148,7 @@ public function fetchNext()
     /**
      * {@inheritdoc}
      */
-    public function hasPrevious()
+    public function hasPrevious(): bool
     {
         return isset($this->pagination['prev']);
     }
@@ -154,7 +156,7 @@ public function hasPrevious()
     /**
      * {@inheritdoc}
      */
-    public function fetchPrevious()
+    public function fetchPrevious(): array
     {
         return $this->get('prev');
     }
@@ -162,7 +164,7 @@ public function fetchPrevious()
     /**
      * {@inheritdoc}
      */
-    public function fetchFirst()
+    public function fetchFirst(): array
     {
         return $this->get('first');
     }
@@ -170,7 +172,7 @@ public function fetchFirst()
     /**
      * {@inheritdoc}
      */
-    public function fetchLast()
+    public function fetchLast(): array
     {
         return $this->get('last');
     }
@@ -180,7 +182,7 @@ public function fetchLast()
      *
      * @return array
      */
-    protected function get(string $key)
+    protected function get(string $key): array
     {
         if (!isset($this->pagination[$key])) {
             return [];
diff --git a/lib/Github/ResultPagerInterface.php b/lib/Github/ResultPagerInterface.php
index 5faf1cb0f53..350f8453e05 100644
--- a/lib/Github/ResultPagerInterface.php
+++ b/lib/Github/ResultPagerInterface.php
@@ -2,6 +2,7 @@
 
 namespace Github;
 
+use Generator;
 use Github\Api\AbstractApi;
 
 /**
@@ -22,7 +23,7 @@ interface ResultPagerInterface
      *
      * @return array returns the result of the Api::$method() call
      */
-    public function fetch(AbstractApi $api, string $method, array $parameters = []);
+    public function fetch(AbstractApi $api, string $method, array $parameters = []): array;
 
     /**
      * Fetch all results (pages) from an api call.
@@ -35,7 +36,7 @@ public function fetch(AbstractApi $api, string $method, array $parameters = []);
      *
      * @return array returns a merge of the results of the Api::$method() call
      */
-    public function fetchAll(AbstractApi $api, string $method, array $parameters = []);
+    public function fetchAll(AbstractApi $api, string $method, array $parameters = []): array;
 
     /**
      * Lazily fetch all results (pages) from an api call.
@@ -48,54 +49,54 @@ public function fetchAll(AbstractApi $api, string $method, array $parameters = [
      *
      * @return \Generator returns a merge of the results of the Api::$method() call
      */
-    public function fetchAllLazy(AbstractApi $api, string $method, array $parameters = []);
+    public function fetchAllLazy(AbstractApi $api, string $method, array $parameters = []): Generator;
 
     /**
      * Method that performs the actual work to refresh the pagination property.
      *
      * @return void
      */
-    public function postFetch();
+    public function postFetch(): void;
 
     /**
      * Check to determine the availability of a next page.
      *
      * @return bool
      */
-    public function hasNext();
+    public function hasNext(): bool;
 
     /**
      * Check to determine the availability of a previous page.
      *
      * @return bool
      */
-    public function hasPrevious();
+    public function hasPrevious(): bool;
 
     /**
      * Fetch the next page.
      *
      * @return array
      */
-    public function fetchNext();
+    public function fetchNext(): array;
 
     /**
      * Fetch the previous page.
      *
      * @return array
      */
-    public function fetchPrevious();
+    public function fetchPrevious(): array;
 
     /**
      * Fetch the first page.
      *
      * @return array
      */
-    public function fetchFirst();
+    public function fetchFirst(): array;
 
     /**
      * Fetch the last page.
      *
      * @return array
      */
-    public function fetchLast();
+    public function fetchLast(): array;
 }
diff --git a/test/Github/Tests/ResultPagerTest.php b/test/Github/Tests/ResultPagerTest.php
index d7d176f4b78..b29626bf5b0 100644
--- a/test/Github/Tests/ResultPagerTest.php
+++ b/test/Github/Tests/ResultPagerTest.php
@@ -110,7 +110,7 @@ public function shouldGetAllSearchResults()
 
     public function testFetch()
     {
-        $result = 'foo';
+        $result = ['foo'];
         $method = 'all';
         $parameters = ['baz'];
         $api = $this->getMockBuilder(Members::class)