diff --git a/lib/BasicResolver.php b/lib/BasicResolver.php
index 00355f4..0bccda9 100644
--- a/lib/BasicResolver.php
+++ b/lib/BasicResolver.php
@@ -9,7 +9,6 @@ use Amp\MultiReasonException;
 use Amp\Promise;
 use Amp\Success;
 use LibDNS\Messages\Message;
-use LibDNS\Messages\MessageTypes;
 use LibDNS\Records\Question;
 use LibDNS\Records\QuestionFactory;
 use function Amp\call;
@@ -51,6 +50,10 @@ final class BasicResolver implements Resolver {
         $this->questionFactory = new QuestionFactory;
 
         $this->gcWatcher = Loop::repeat(5000, function () {
+            if (empty($this->servers)) {
+                return;
+            }
+
             $now = \time();
 
             foreach ($this->servers as $key => $server) {
@@ -183,21 +186,21 @@ final class BasicResolver implements Resolver {
 
             $nameservers = $this->config->getNameservers();
             $attempts = $this->config->getAttempts();
-            $receivedTruncatedResponse = false;
+            $protocol = "udp";
+            $attempt = 0;
 
-            for ($attempt = 0; $attempt < $attempts; ++$attempt) {
-                $i = $attempt % \count($nameservers);
-                $protocol = $receivedTruncatedResponse ? "tcp" : "udp";
+            /** @var Server $server */
+            $uri = $protocol . "://" . $nameservers[0];
+            $server = yield $this->getServer($uri);
 
+            while ($attempt < $attempts) {
                 try {
-                    /** @var \Amp\Dns\Server $server */
-                    $server = yield $this->getServer($protocol . "://" . $nameservers[$i]);
-
                     if (!$server->isAlive()) {
-                        $this->servers[$protocol . "://" . $nameservers[$i]]->close();
-                        unset($this->servers[$protocol . "://" . $nameservers[$i]]);
+                        unset($this->servers[$uri]);
+                        $server->close();
 
                         /** @var \Amp\Dns\Server $server */
+                        $i = $attempt % \count($nameservers);
                         $server = yield $this->getServer($protocol . "://" . $nameservers[$i]);
                     }
 
@@ -206,10 +209,11 @@ final class BasicResolver implements Resolver {
                     $this->assertAcceptableResponse($response);
 
                     if ($response->isTruncated()) {
-                        if (!$receivedTruncatedResponse) {
+                        if ($protocol !== "tcp") {
                             // Retry with TCP, don't count attempt
-                            $receivedTruncatedResponse = true;
-                            $attempt--;
+                            $protocol = "tcp";
+                            $i = $attempt % \count($nameservers);
+                            $server = yield $this->getServer($protocol . "://" . $nameservers[$i]);
                             continue;
                         }
 
@@ -244,6 +248,9 @@ final class BasicResolver implements Resolver {
                         return new Record($data, $type, $ttls[$type]);
                     }, $result[$type]);
                 } catch (TimeoutException $e) {
+                    $i = ++$attempt % \count($nameservers);
+                    $server = yield $this->getServer($protocol . "://" . $nameservers[$i]);
+
                     continue;
                 }
             }
@@ -327,6 +334,10 @@ final class BasicResolver implements Resolver {
     }
 
     private function getServer($uri): Promise {
+        if (\substr($uri, 0, 3) === "udp") {
+            return UdpServer::connect($uri);
+        }
+
         if (isset($this->servers[$uri])) {
             return new Success($this->servers[$uri]);
         }
@@ -335,16 +346,12 @@ final class BasicResolver implements Resolver {
             return $this->pendingServers[$uri];
         }
 
-        if (\substr($uri, 0, 3) === "udp") {
-            $server = UdpServer::connect($uri);
-        } else {
-            $server = TcpServer::connect($uri);
-        }
+        $server = TcpServer::connect($uri);
 
         $server->onResolve(function ($error, $server) use ($uri) {
-            if ($error) {
-                unset($this->pendingServers[$uri]);
-            } else {
+            unset($this->pendingServers[$uri]);
+
+            if (!$error) {
                 $this->servers[$uri] = $server;
             }
         });
diff --git a/lib/Server.php b/lib/Server.php
index 59916ea..59cdf5e 100644
--- a/lib/Server.php
+++ b/lib/Server.php
@@ -16,6 +16,8 @@ use function Amp\call;
 
 /** @internal */
 abstract class Server {
+    const MAX_CONCURRENT_REQUESTS = 500;
+
     /** @var ResourceInputStream */
     private $input;
 
@@ -28,9 +30,6 @@ abstract class Server {
     /** @var MessageFactory */
     private $messageFactory;
 
-    /** @var int */
-    private $nextId = 0;
-
     /** @var callable */
     private $onResolve;
 
@@ -40,6 +39,9 @@ abstract class Server {
     /** @var bool */
     private $receiving = false;
 
+    /** @var array */
+    private $queue = [];
+
     /**
      * @param string $uri
      *
@@ -113,17 +115,15 @@ abstract class Server {
         return call(function () use ($question, $timeout) {
             $this->lastActivity = \time();
 
-            $id = $this->nextId++;
-            if ($this->nextId > 0xffff) {
-                $this->nextId %= 0xffff;
+            if (\count($this->pending) > self::MAX_CONCURRENT_REQUESTS) {
+                $deferred = new Deferred;
+                $this->queue[] = $deferred;
+                yield $deferred->promise();
             }
 
-            if (isset($this->pending[$id])) {
-                /** @var Deferred $deferred */
-                $deferred = $this->pending[$id]->deferred;
-                unset($this->pending[$id]);
-                $deferred->fail(new ResolutionException("Request hasn't been answered with 65k requests in between"));
-            }
+            do {
+                $id = \random_int(0, 0xffff);
+            } while (isset($this->pending[$id]));
 
             $message = $this->createMessage($question, $id);
 
@@ -158,10 +158,17 @@ abstract class Server {
                 return yield Promise\timeout($deferred->promise(), $timeout);
             } catch (Amp\TimeoutException $exception) {
                 unset($this->pending[$id]);
+
                 if (empty($this->pending)) {
                     $this->input->unreference();
                 }
+
                 throw new TimeoutException("Didn't receive a response within {$timeout} milliseconds.");
+            } finally {
+                if ($this->queue) {
+                    $deferred = array_shift($this->queue);
+                    $deferred->resolve();
+                }
             }
         });
     }