diff --git a/src/Query/TcpTransportExecutor.php b/src/Query/TcpTransportExecutor.php
index bfaedbae..669fd012 100644
--- a/src/Query/TcpTransportExecutor.php
+++ b/src/Query/TcpTransportExecutor.php
@@ -134,7 +134,7 @@ class TcpTransportExecutor implements ExecutorInterface
      * @param string         $nameserver
      * @param ?LoopInterface $loop
      */
-    public function __construct($nameserver, LoopInterface $loop = null)
+    public function __construct($nameserver, $loop = null)
     {
         if (\strpos($nameserver, '[') === false && \substr_count($nameserver, ':') >= 2 && \strpos($nameserver, '://') === false) {
             // several colons, but not enclosed in square brackets => enclose IPv6 address in square brackets
@@ -146,6 +146,10 @@ public function __construct($nameserver, LoopInterface $loop = null)
             throw new \InvalidArgumentException('Invalid nameserver address given');
         }
 
+        if ($loop !== null && !$loop instanceof LoopInterface) { // manual type check to support legacy PHP < 7.1
+            throw new \InvalidArgumentException('Argument #2 ($loop) expected null|React\EventLoop\LoopInterface');
+        }
+
         $this->nameserver = 'tcp://' . $parts['host'] . ':' . (isset($parts['port']) ? $parts['port'] : 53);
         $this->loop = $loop ?: Loop::get();
         $this->parser = new Parser();
diff --git a/src/Query/TimeoutExecutor.php b/src/Query/TimeoutExecutor.php
index 06c51b15..76bd864e 100644
--- a/src/Query/TimeoutExecutor.php
+++ b/src/Query/TimeoutExecutor.php
@@ -12,8 +12,15 @@ final class TimeoutExecutor implements ExecutorInterface
     private $loop;
     private $timeout;
 
-    public function __construct(ExecutorInterface $executor, $timeout, LoopInterface $loop = null)
+    /**
+     * @param ?LoopInterface $loop
+     */
+    public function __construct(ExecutorInterface $executor, $timeout, $loop = null)
     {
+        if ($loop !== null && !$loop instanceof LoopInterface) { // manual type check to support legacy PHP < 7.1
+            throw new \InvalidArgumentException('Argument #3 ($loop) expected null|React\EventLoop\LoopInterface');
+        }
+
         $this->executor = $executor;
         $this->loop = $loop ?: Loop::get();
         $this->timeout = $timeout;
diff --git a/src/Query/UdpTransportExecutor.php b/src/Query/UdpTransportExecutor.php
index 30a3d705..a8cbfafa 100644
--- a/src/Query/UdpTransportExecutor.php
+++ b/src/Query/UdpTransportExecutor.php
@@ -98,7 +98,7 @@ final class UdpTransportExecutor implements ExecutorInterface
      * @param string         $nameserver
      * @param ?LoopInterface $loop
      */
-    public function __construct($nameserver, LoopInterface $loop = null)
+    public function __construct($nameserver, $loop = null)
     {
         if (\strpos($nameserver, '[') === false && \substr_count($nameserver, ':') >= 2 && \strpos($nameserver, '://') === false) {
             // several colons, but not enclosed in square brackets => enclose IPv6 address in square brackets
@@ -110,6 +110,10 @@ public function __construct($nameserver, LoopInterface $loop = null)
             throw new \InvalidArgumentException('Invalid nameserver address given');
         }
 
+        if ($loop !== null && !$loop instanceof LoopInterface) { // manual type check to support legacy PHP < 7.1
+            throw new \InvalidArgumentException('Argument #2 ($loop) expected null|React\EventLoop\LoopInterface');
+        }
+
         $this->nameserver = 'udp://' . $parts['host'] . ':' . (isset($parts['port']) ? $parts['port'] : 53);
         $this->loop = $loop ?: Loop::get();
         $this->parser = new Parser();
diff --git a/src/Resolver/Factory.php b/src/Resolver/Factory.php
index 5fe608cb..52658951 100644
--- a/src/Resolver/Factory.php
+++ b/src/Resolver/Factory.php
@@ -36,8 +36,12 @@ final class Factory
      * @throws \InvalidArgumentException for invalid DNS server address
      * @throws \UnderflowException when given DNS Config object has an empty list of nameservers
      */
-    public function create($config, LoopInterface $loop = null)
+    public function create($config, $loop = null)
     {
+        if ($loop !== null && !$loop instanceof LoopInterface) { // manual type check to support legacy PHP < 7.1
+            throw new \InvalidArgumentException('Argument #2 ($loop) expected null|React\EventLoop\LoopInterface');
+        }
+
         $executor = $this->decorateHostsFileExecutor($this->createExecutor($config, $loop ?: Loop::get()));
 
         return new Resolver($executor);
@@ -59,8 +63,16 @@ public function create($config, LoopInterface $loop = null)
      * @throws \InvalidArgumentException for invalid DNS server address
      * @throws \UnderflowException when given DNS Config object has an empty list of nameservers
      */
-    public function createCached($config, LoopInterface $loop = null, CacheInterface $cache = null)
+    public function createCached($config, $loop = null, $cache = null)
     {
+        if ($loop !== null && !$loop instanceof LoopInterface) { // manual type check to support legacy PHP < 7.1
+            throw new \InvalidArgumentException('Argument #2 ($loop) expected null|React\EventLoop\LoopInterface');
+        }
+
+        if ($cache !== null && !$cache instanceof CacheInterface) { // manual type check to support legacy PHP < 7.1
+            throw new \InvalidArgumentException('Argument #3 ($cache) expected null|React\Cache\CacheInterface');
+        }
+
         // default to keeping maximum of 256 responses in cache unless explicitly given
         if (!($cache instanceof CacheInterface)) {
             $cache = new ArrayCache(256);
diff --git a/tests/Query/TcpTransportExecutorTest.php b/tests/Query/TcpTransportExecutorTest.php
index 33dddacd..6c25a6db 100644
--- a/tests/Query/TcpTransportExecutorTest.php
+++ b/tests/Query/TcpTransportExecutorTest.php
@@ -943,4 +943,11 @@ public function testQueryAgainAfterPreviousQueryResolvedWillReuseSocketAndCancel
         // trigger second query
         $executor->query($query);
     }
+
+    /** @test */
+    public function constructorThrowsExceptionForInvalidLoop()
+    {
+        $this->setExpectedException('InvalidArgumentException', 'Argument #2 ($loop) expected null|React\EventLoop\LoopInterface');
+        new TcpTransportExecutor('tcp://127.0.0.1:53', 'loop');
+    }
 }
diff --git a/tests/Query/TimeoutExecutorTest.php b/tests/Query/TimeoutExecutorTest.php
index b7857783..e4ed5788 100644
--- a/tests/Query/TimeoutExecutorTest.php
+++ b/tests/Query/TimeoutExecutorTest.php
@@ -185,4 +185,11 @@ public function testRejectsPromiseAndCancelsPendingQueryWhenTimeoutTriggers()
         $this->assertInstanceOf('React\Dns\Query\TimeoutException', $exception);
         $this->assertEquals('DNS query for igor.io (A) timed out' , $exception->getMessage());
     }
+
+    /** @test */
+    public function constructorThrowsExceptionForInvalidLoop()
+    {
+        $this->setExpectedException('InvalidArgumentException', 'Argument #3 ($loop) expected null|React\EventLoop\LoopInterface');
+        new TimeoutExecutor($this->executor, 5.0, 'loop');
+    }
 }
diff --git a/tests/Query/UdpTransportExecutorTest.php b/tests/Query/UdpTransportExecutorTest.php
index 3f04d9ad..eb1afbaf 100644
--- a/tests/Query/UdpTransportExecutorTest.php
+++ b/tests/Query/UdpTransportExecutorTest.php
@@ -375,4 +375,11 @@ public function testQueryResolvesIfServerSendsValidResponse()
 
         $this->assertInstanceOf('React\Dns\Model\Message', $response);
     }
+
+    /** @test */
+    public function constructorThrowsExceptionForInvalidLoop()
+    {
+        $this->setExpectedException('InvalidArgumentException', 'Argument #2 ($loop) expected null|React\EventLoop\LoopInterface');
+        new UdpTransportExecutor('udp://127.0.0.1:53', 'loop');
+    }
 }
diff --git a/tests/Resolver/FactoryTest.php b/tests/Resolver/FactoryTest.php
index af758b51..585ee985 100644
--- a/tests/Resolver/FactoryTest.php
+++ b/tests/Resolver/FactoryTest.php
@@ -399,6 +399,32 @@ public function createCachedShouldCreateResolverWithCachingExecutorWithCustomCac
         $this->assertSame($cache, $cacheProperty);
     }
 
+    /** @test */
+    public function createThrowsExceptionForInvalidLoop()
+    {
+        $this->setExpectedException('InvalidArgumentException', 'Argument #2 ($loop) expected null|React\EventLoop\LoopInterface');
+        $factory = new Factory();
+        $factory->create('config', 'loop');
+    }
+
+    /** @test */
+    public function createCachedThrowsExceptionForInvalidLoop()
+    {
+        $this->setExpectedException('InvalidArgumentException', 'Argument #2 ($loop) expected null|React\EventLoop\LoopInterface');
+        $factory = new Factory();
+        $factory->createCached('config', 'loop');
+    }
+
+    /** @test */
+    public function createCachedThrowsExceptionForInvalidCache()
+    {
+        $loop = $this->getMockBuilder('React\EventLoop\LoopInterface')->getMock();
+
+        $this->setExpectedException('InvalidArgumentException', 'Argument #3 ($cache) expected null|React\Cache\CacheInterface');
+        $factory = new Factory();
+        $factory->createCached('config', $loop, 'cache');
+    }
+
     private function getResolverPrivateExecutor($resolver)
     {
         $executor = $this->getResolverPrivateMemberValue($resolver, 'executor');