diff --git a/composer.json b/composer.json
index 7603398..5e2a479 100644
--- a/composer.json
+++ b/composer.json
@@ -41,7 +41,7 @@
         }
     ],
     "require": {
-        "php": ">=7.0",
+        "php": ">=8.1",
         "amphp/cache": "^v2-dev",
         "amphp/parser": "^1",
         "danog/libdns-json": "^0.1",
diff --git a/lib/DoHConfig.php b/lib/DoHConfig.php
index 793eb45..2f1f657 100644
--- a/lib/DoHConfig.php
+++ b/lib/DoHConfig.php
@@ -15,7 +15,7 @@ use Amp\Http\Client\HttpClientBuilder;
 final class DoHConfig
 {
     /**
-     * @var non-empty-array<NameServer> $nameservers
+     * @var non-empty-array<Nameserver> $nameservers
      */
     private readonly array $nameservers;
     private readonly DelegateHttpClient $httpClient;
@@ -24,15 +24,17 @@ final class DoHConfig
     private readonly Cache $cache;
 
     /**
-     * @param non-empty-array<NameServer> $nameservers
+     * @param non-empty-array<Nameserver> $nameservers
      */
     public function __construct(array $nameservers, ?DelegateHttpClient $httpClient = null, ?Rfc1035StubResolver $resolver = null, ?ConfigLoader $configLoader = null, ?Cache $cache = null)
     {
+        /** @psalm-suppress TypeDoesNotContainType */
         if (\count($nameservers) < 1) {
             throw new ConfigException("At least one nameserver is required for a valid config");
         }
 
         foreach ($nameservers as $nameserver) {
+            /** @psalm-suppress DocblockContradiction */
             if (!($nameserver instanceof Nameserver)) {
                 throw new ConfigException("Invalid nameserver: {$nameserver}");
             }
diff --git a/lib/Nameserver.php b/lib/Nameserver.php
index e118984..583fc11 100644
--- a/lib/Nameserver.php
+++ b/lib/Nameserver.php
@@ -6,6 +6,10 @@ use Amp\Dns\ConfigException;
 
 final class Nameserver
 {
+    public const RFC8484_GET = NameserverType::RFC8484_GET;
+    public const RFC8484_POST = NameserverType::RFC8484_POST;
+    public const GOOGLE_JSON = NameserverType::GOOGLE_JSON;
+
     private readonly string $host;
 
     public function __construct(
diff --git a/lib/Rfc8484StubResolver.php b/lib/Rfc8484StubResolver.php
index bc7d6fa..3dba1de 100644
--- a/lib/Rfc8484StubResolver.php
+++ b/lib/Rfc8484StubResolver.php
@@ -18,10 +18,8 @@ use Amp\Future;
 use Amp\Http\Client\DelegateHttpClient;
 use Amp\Http\Client\Request;
 use Amp\NullCancellation;
-use Amp\Promise;
 use danog\LibDNSJson\JsonDecoder;
 use danog\LibDNSJson\JsonDecoderFactory;
-use danog\LibDNSJson\QueryEncoder;
 use danog\LibDNSJson\QueryEncoderFactory;
 use LibDNS\Decoder\Decoder;
 use LibDNS\Decoder\DecoderFactory;
@@ -48,13 +46,13 @@ final class Rfc8484StubResolver implements Resolver
 
     private Cache $cache;
 
-    /** @var Promise[] */
+    /** @var Future[] */
     private array $pendingQueries = [];
 
     private Rfc1035StubResolver $subResolver;
     private Encoder $encoder;
     private Decoder $decoder;
-    private QueryEncoder $encoderJson;
+    private Encoder $encoderJson;
     private JsonDecoder $decoderJson;
     private MessageFactory $messageFactory;
     private DelegateHttpClient $httpClient;
@@ -234,6 +232,7 @@ final class Rfc8484StubResolver implements Resolver
 
     private function queryHosts(string $name, int $typeRestriction = null): array
     {
+        \assert($this->config !== null);
         $hosts = $this->config->getKnownHosts();
         $records = [];
 
@@ -271,6 +270,8 @@ final class Rfc8484StubResolver implements Resolver
                     }
                 }
 
+                \assert($this->config !== null);
+
                 $name = $this->normalizeName($name, $type);
                 $question = $this->createQuestion($name, $type);
 
@@ -301,7 +302,6 @@ final class Rfc8484StubResolver implements Resolver
                         $result = [];
                         $ttls = [];
 
-                        /** @var \LibDNS\Records\Resource $record */
                         foreach ($answers as $record) {
                             $recordType = $record->getType();
                             $result[$recordType][] = (string) $record->getData();
@@ -351,6 +351,7 @@ final class Rfc8484StubResolver implements Resolver
     private function ask(Nameserver $nameserver, Question $question, Cancellation $cancellation): Message
     {
         $message = $this->createMessage($question, \random_int(0, 0xffff));
+        $request = null;
         switch ($nameserver->getType()) {
             case NameserverType::RFC8484_GET:
                 $data = $this->encoder->encode($message);
@@ -364,7 +365,7 @@ final class Rfc8484StubResolver implements Resolver
                 $request->setBody($data);
                 $request->setHeader('content-type', 'application/dns-message');
                 $request->setHeader('accept', 'application/dns-message');
-                $request->setHeader('content-length', \strlen($data));
+                $request->setHeader('content-length', (string) \strlen($data));
                 $request->setHeaders($nameserver->getHeaders());
                 break;
             case NameserverType::GOOGLE_JSON:
@@ -374,6 +375,7 @@ final class Rfc8484StubResolver implements Resolver
                 $request->setHeaders($nameserver->getHeaders());
                 break;
         }
+        \assert($request !== null);
 
         $response = $this->httpClient->request($request, $cancellation);
         if ($response->getStatus() !== 200) {
@@ -390,7 +392,7 @@ final class Rfc8484StubResolver implements Resolver
         }
     }
 
-    private function normalizeName(string $name, int $type)
+    private function normalizeName(string $name, int $type): string
     {
         if ($type === Record::PTR) {
             if (($packedIp = @\inet_pton($name)) !== false) {
@@ -434,7 +436,10 @@ final class Rfc8484StubResolver implements Resolver
         return self::CACHE_PREFIX.$name."#".$type;
     }
 
-    private function decodeCachedResult(string $name, int $type, string $encoded)
+    /**
+     * @return list<Record>
+     */
+    private function decodeCachedResult(string $name, int $type, string $encoded): array
     {
         $decoded = \json_decode($encoded, true);
 
diff --git a/psalm.xml b/psalm.xml
new file mode 100644
index 0000000..d6746fa
--- /dev/null
+++ b/psalm.xml
@@ -0,0 +1,15 @@
+<?xml version="1.0"?>
+<psalm
+    errorLevel="2"
+    resolveFromConfigFile="true"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns="https://getpsalm.org/schema/config"
+    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
+>
+    <projectFiles>
+        <directory name="lib" />
+        <ignoreFiles>
+            <directory name="vendor" />
+        </ignoreFiles>
+    </projectFiles>
+</psalm>