diff --git a/composer.json b/composer.json
index 2923c55..7788b7d 100644
--- a/composer.json
+++ b/composer.json
@@ -12,16 +12,16 @@
     ],
     "require": {
         "php": ">=5.3",
-        "react/promise": "^3 || ^2.1 || ^1.2.1",
-        "react/socket": "^1.12",
+        "react/promise": "^3.2 || ^2.1 || ^1.2.1",
+        "react/socket": "^1.16",
         "ringcentral/psr7": "^1.2"
     },
     "require-dev": {
         "phpunit/phpunit": "^9.6 || ^5.7 || ^4.8.36",
-        "react/async": "^4 || ^3 || ^2",
+        "react/async": "^4.3 || ^3 || ^2",
         "react/event-loop": "^1.2",
-        "react/http": "^1.5",
-        "react/promise-timer": "^1.10"
+        "react/http": "^1.11",
+        "react/promise-timer": "^1.11"
     },
     "autoload": {
         "psr-4": { 
diff --git a/src/ProxyConnector.php b/src/ProxyConnector.php
index d7f2863..0e7bcdb 100644
--- a/src/ProxyConnector.php
+++ b/src/ProxyConnector.php
@@ -60,7 +60,7 @@ class ProxyConnector implements ConnectorInterface
     public function __construct(
         #[\SensitiveParameter]
         $proxyUrl,
-        ConnectorInterface $connector = null,
+        $connector = null,
         array $httpHeaders = array()
     ) {
         // support `http+unix://` scheme for Unix domain socket (UDS) paths
@@ -84,6 +84,10 @@ public function __construct(
             throw new InvalidArgumentException('Invalid proxy URL "' . $proxyUrl . '"');
         }
 
+        if ($connector !== null && !$connector instanceof ConnectorInterface) { // manual type check to support legacy PHP < 7.1
+            throw new \InvalidArgumentException('Argument #2 ($connector) expected null|React\Socket\ConnectorInterface');
+        }
+
         // apply default port and TCP/TLS transport for given scheme
         if (!isset($parts['port'])) {
             $parts['port'] = $parts['scheme'] === 'https' ? 443 : 80;
diff --git a/tests/ProxyConnectorTest.php b/tests/ProxyConnectorTest.php
index f2d5795..0839692 100644
--- a/tests/ProxyConnectorTest.php
+++ b/tests/ProxyConnectorTest.php
@@ -48,6 +48,12 @@ public function testInvalidHttpsUnixScheme()
         new ProxyConnector('https+unix:///tmp/proxy.sock', $this->connector);
     }
 
+    public function testContructorThrowsExceptionForInvalidConnector()
+    {
+        $this->setExpectedException('InvalidArgumentException', 'Argument #2 ($connector) expected null|React\Socket\ConnectorInterface');
+        new ProxyConnector('proxy.example.com', 'connector');
+    }
+
     public function testCreatesConnectionToHttpPort()
     {
         $promise = new Promise(function () { });