diff --git a/.styleci.yml b/.styleci.yml
index 5328b61..2c1e770 100644
--- a/.styleci.yml
+++ b/.styleci.yml
@@ -12,3 +12,4 @@ enabled:
 
 disabled:
     - phpdoc_annotation_without_dot # This is still buggy: https://github.com/symfony/symfony/pull/19198
+    - single_line_throw
diff --git a/CHANGELOG.md b/CHANGELOG.md
index b2202bb..f034858 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,12 +1,19 @@
 # Change Log
 
-## 1.4.0 -
+## 1.4.0 - 2020-07-02
+
+### Added
+
+- Support for the PSR-17 response factory
+
+### Changed
+
+- Drop support for PHP 5 and 7.0
+- Consitent implementation of union type checking
 
 ### Fixed
-- `reset()` should not trigger `setDefaultException` error condition
 
-### Breaking
-- drop support for PHP 5 and 7.0
+- `reset()` should not trigger `setDefaultException` error condition
 
 ## 1.3.1 - 2019-11-06
 
diff --git a/composer.json b/composer.json
index 662387c..cc60787 100644
--- a/composer.json
+++ b/composer.json
@@ -20,7 +20,11 @@
         "php-http/client-common": "^1.9 || ^2.0",
         "php-http/discovery": "^1.0",
         "php-http/httplug": "^1.0 || ^2.0",
-        "php-http/message-factory": "^1.0"
+        "php-http/message-factory": "^1.0",
+        "psr/http-client": "^1.0",
+        "psr/http-factory": "^1.0",
+        "psr/http-message": "^1.0",
+        "symfony/polyfill-php80": "^1.17"
     },
     "provide": {
         "php-http/async-client-implementation": "1.0",
diff --git a/spec/ClientSpec.php b/spec/ClientSpec.php
index f72481e..b5ee678 100644
--- a/spec/ClientSpec.php
+++ b/spec/ClientSpec.php
@@ -7,6 +7,7 @@
 use Http\Message\RequestMatcher;
 use Http\Message\ResponseFactory;
 use Http\Mock\Client;
+use Psr\Http\Client\ClientExceptionInterface;
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
 use PhpSpec\ObjectBehavior;
@@ -49,16 +50,16 @@ function it_returns_the_default_response_for_a_request(RequestInterface $request
 
     function it_throws_an_exception_for_a_request(RequestInterface $request)
     {
-        $this->addException(new \Exception());
+        $this->addException(new Exception());
 
-        $this->shouldThrow('Exception')->duringSendRequest($request);
+        $this->shouldThrow(Exception::class)->duringSendRequest($request);
     }
 
     function it_throws_the_default_exception_for_a_request(RequestInterface $request)
     {
-        $this->setDefaultException(new \Exception());
+        $this->setDefaultException(new Exception());
 
-        $this->shouldThrow('Exception')->duringSendRequest($request);
+        $this->shouldThrow(Exception::class)->duringSendRequest($request);
     }
 
     function it_creates_an_empty_response_when_none_is_added(
@@ -94,8 +95,8 @@ function it_reset(
     ) {
         $this->addResponse($response);
         $this->setDefaultResponse($response);
-        $this->addException(new \Exception());
-        $this->setDefaultException(new \Exception());
+        $this->addException(new Exception());
+        $this->setDefaultException(new Exception());
 
         $responseFactory->createResponse()->willReturn($newResponse);
 
@@ -122,8 +123,8 @@ function it_throws_exception_if_request_matcher_matches(
         RequestInterface $request
     ) {
         $matcher->matches($request)->willReturn(true);
-        $this->on($matcher, new \Exception());
-        $this->shouldThrow('Exception')->duringSendRequest($request);
+        $this->on($matcher, new Exception());
+        $this->shouldThrow(Exception::class)->duringSendRequest($request);
     }
 
     function it_skips_conditional_response_if_matcher_returns_false(
@@ -155,3 +156,7 @@ function(RequestInterface $request) use ($response) {
         $this->sendRequest($request)->shouldReturn($response);
     }
 }
+
+class Exception extends \Exception implements ClientExceptionInterface
+{
+}
diff --git a/src/Client.php b/src/Client.php
index 1b3782b..7f6a606 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -12,6 +12,7 @@
 use Http\Message\ResponseFactory;
 use Psr\Http\Client\ClientExceptionInterface;
 use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseFactoryInterface;
 use Psr\Http\Message\ResponseInterface;
 
 /**
@@ -28,7 +29,7 @@ class Client implements HttpClient, HttpAsyncClient
     use VersionBridgeClient;
 
     /**
-     * @var ResponseFactory
+     * @var ResponseFactory|ResponseFactoryInterface
      */
     private $responseFactory;
 
@@ -62,8 +63,17 @@ class Client implements HttpClient, HttpAsyncClient
      */
     private $defaultException;
 
-    public function __construct(ResponseFactory $responseFactory = null)
+    /**
+     * @param ResponseFactory|ResponseFactoryInterface|null
+     */
+    public function __construct($responseFactory = null)
     {
+        if (!$responseFactory instanceof ResponseFactory && !$responseFactory instanceof ResponseFactoryInterface && null !== $responseFactory) {
+            throw new \TypeError(
+                sprintf('%s::__construct(): Argument #1 ($responseFactory) must be of type %s|%s|null, %s given', self::class, ResponseFactory::class, ResponseFactoryInterface::class, get_debug_type($responseFactory))
+            );
+        }
+
         $this->responseFactory = $responseFactory ?: MessageFactoryDiscovery::find();
     }
 
@@ -122,6 +132,12 @@ public function doSendRequest(RequestInterface $request)
      */
     public function on(RequestMatcher $requestMatcher, $result)
     {
+        if (!$result instanceof ResponseInterface && !$result instanceof Exception && !$result instanceof ClientExceptionInterface && !is_callable($result)) {
+            throw new \TypeError(
+                sprintf('%s::on(): Argument #2 ($result) must be of type %s|%s|%s|callable, %s given', self::class, ResponseInterface::class, Exception::class, ClientExceptionInterface::class, get_debug_type($result))
+            );
+        }
+
         $callable = self::makeCallable($result);
 
         $this->conditionalResults[] = [
@@ -133,8 +149,6 @@ public function on(RequestMatcher $requestMatcher, $result)
     /**
      * @param ResponseInterface|Exception|ClientExceptionInterface|callable $result
      *
-     * @throws \InvalidArgumentException
-     *
      * @return callable
      */
     private static function makeCallable($result)
@@ -149,13 +163,9 @@ private static function makeCallable($result)
             };
         }
 
-        if ($result instanceof \Exception) {
-            return function () use ($result) {
-                throw $result;
-            };
-        }
-
-        throw new \InvalidArgumentException('Result must be either a response, an exception, or a callable');
+        return function () use ($result) {
+            throw $result;
+        };
     }
 
     /**