diff --git a/composer.json b/composer.json
index 3b7e7e6..4e3d19b 100644
--- a/composer.json
+++ b/composer.json
@@ -33,7 +33,8 @@
         "amphp/amp": "^1",
         "amphp/cache": "^0.1",
         "amphp/file": "^0.1",
-        "daverandom/libdns": "^1"
+        "daverandom/libdns": "^1",
+        "paragonie/random_compat": "^1"
     },
     "require-dev": {
         "phpunit/phpunit": "^4.8",
diff --git a/lib/DefaultResolver.php b/lib/DefaultResolver.php
index 3466ba6..e4aaf24 100644
--- a/lib/DefaultResolver.php
+++ b/lib/DefaultResolver.php
@@ -21,7 +21,6 @@ class DefaultResolver implements Resolver {
     private $encoder;
     private $decoder;
     private $arrayCache;
-    private $requestIdCounter;
     private $pendingRequests;
     private $serverIdMap;
     private $serverUriMap;
@@ -36,7 +35,6 @@ class DefaultResolver implements Resolver {
         $this->encoder = (new EncoderFactory)->create();
         $this->decoder = (new DecoderFactory)->create();
         $this->arrayCache = new ArrayCache;
-        $this->requestIdCounter = 1;
         $this->pendingRequests = [];
         $this->serverIdMap = [];
         $this->serverUriMap = [];
@@ -159,11 +157,15 @@ class DefaultResolver implements Resolver {
         $server = $this->loadExistingServer($uri) ?: $this->loadNewServer($uri);
 
         // Get the next available request ID
+        if (\count($this->pendingRequests) > MAX_REQUEST_ID / 2) {
+            // throttle DNS requests as long as too many requests are active
+            return \Amp\pipe(\Amp\Pause(100), function () use ($uri, $name, $type) {
+                return $this->doRequest($uri, $name, $type);
+            });
+        }
+
         do {
-            $requestId = $this->requestIdCounter++;
-            if ($this->requestIdCounter >= MAX_REQUEST_ID) {
-                $this->requestIdCounter = 1;
-            }
+            $requestId = random_int(0, MAX_REQUEST_ID - 1);
         } while (isset($this->pendingRequests[$requestId]));
 
         // Create question record