diff --git a/composer.json b/composer.json
index 49e4dc2..5bec52c 100644
--- a/composer.json
+++ b/composer.json
@@ -20,7 +20,7 @@
         "php": ">=5.6",
         "behat/behat": "~3.0",
         "guzzlehttp/guzzle": "4 - 6",
-        "phpunit/phpunit": "4 - 5"
+        "phpunit/phpunit": "4 - 6"
     },
 
     "require-dev": {
diff --git a/features/bootstrap/FeatureContext.php b/features/bootstrap/FeatureContext.php
index 37dc500..db301c3 100644
--- a/features/bootstrap/FeatureContext.php
+++ b/features/bootstrap/FeatureContext.php
@@ -2,6 +2,7 @@
 
 use Behat\Behat\Context\SnippetAcceptingContext;
 use Behat\Gherkin\Node\PyStringNode;
+use PHPUnit\Framework\Assert;
 use Symfony\Component\Process\PhpExecutableFinder;
 use Symfony\Component\Process\Process;
 
@@ -119,7 +120,11 @@ public function itShouldPassWith($success, PyStringNode $text)
      */
     public function theOutputShouldContain(PyStringNode $text)
     {
-        PHPUnit_Framework_Assert::assertContains($this->getExpectedOutput($text), $this->getOutput());
+        if (class_exists(Assert::class)) {
+            Assert::assertContains($this->getExpectedOutput($text), $this->getOutput());
+        } else {
+            PHPUnit_Framework_Assert::assertContains($this->getExpectedOutput($text), $this->getOutput());
+        }
     }
 
     private function getExpectedOutput(PyStringNode $expectedText)
@@ -162,13 +167,21 @@ public function itShouldFail($success)
                 echo 'Actual output:' . PHP_EOL . PHP_EOL . $this->getOutput();
             }
 
-            PHPUnit_Framework_Assert::assertNotEquals(0, $this->getExitCode());
+            if (class_exists(Assert::class)) {
+                Assert::assertNotEquals(0, $this->getExitCode());
+            } else {
+                PHPUnit_Framework_Assert::assertNotEquals(0, $this->getExitCode());
+            }
         } else {
             if (0 !== $this->getExitCode()) {
                 echo 'Actual output:' . PHP_EOL . PHP_EOL . $this->getOutput();
             }
 
-            PHPUnit_Framework_Assert::assertEquals(0, $this->getExitCode());
+            if (class_exists(Assert::class)) {
+                Assert::assertEquals(0, $this->getExitCode());
+            } else {
+                PHPUnit_Framework_Assert::assertEquals(0, $this->getExitCode());
+            }
         }
     }
 
diff --git a/src/Context/WebApiContext.php b/src/Context/WebApiContext.php
index fa008df..97b1231 100644
--- a/src/Context/WebApiContext.php
+++ b/src/Context/WebApiContext.php
@@ -15,6 +15,7 @@
 use GuzzleHttp\ClientInterface;
 use GuzzleHttp\Exception\RequestException;
 use GuzzleHttp\Psr7\Request;
+use PHPUnit\Framework\Assert;
 use PHPUnit_Framework_Assert as Assertions;
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
@@ -219,7 +220,11 @@ public function theResponseCodeShouldBe($code)
     {
         $expected = intval($code);
         $actual = intval($this->response->getStatusCode());
-        Assertions::assertSame($expected, $actual);
+        if (class_exists(Assert::class)) {
+            Assert::assertSame($expected, $actual);
+        } else {
+            Assertions::assertSame($expected, $actual);
+        }
     }
 
     /**
@@ -233,7 +238,11 @@ public function theResponseShouldContain($text)
     {
         $expectedRegexp = '/' . preg_quote($text) . '/i';
         $actual = (string) $this->response->getBody();
-        Assertions::assertRegExp($expectedRegexp, $actual);
+        if (class_exists(Assert::class)) {
+            Assert::assertRegExp($expectedRegexp, $actual);
+        } else {
+            Assertions::assertRegExp($expectedRegexp, $actual);
+        }
     }
 
     /**
@@ -247,7 +256,11 @@ public function theResponseShouldNotContain($text)
     {
         $expectedRegexp = '/' . preg_quote($text) . '/';
         $actual = (string) $this->response->getBody();
-        Assertions::assertNotRegExp($expectedRegexp, $actual);
+        if (class_exists(Assert::class)) {
+            Assert::assertNotRegExp($expectedRegexp, $actual);
+        } else {
+            Assertions::assertNotRegExp($expectedRegexp, $actual);
+        }
     }
 
     /**
@@ -278,10 +291,18 @@ public function theResponseShouldContainJson(PyStringNode $jsonString)
             );
         }
 
-        Assertions::assertGreaterThanOrEqual(count($etalon), count($actual));
-        foreach ($etalon as $key => $needle) {
-            Assertions::assertArrayHasKey($key, $actual);
-            Assertions::assertEquals($etalon[$key], $actual[$key]);
+        if (class_exists(Assert::class)) {
+            Assert::assertGreaterThanOrEqual(count($etalon), count($actual));
+            foreach ($etalon as $key => $needle) {
+                Assert::assertArrayHasKey($key, $actual);
+                Assert::assertEquals($etalon[$key], $actual[$key]);
+            }
+        } else {
+            Assertions::assertGreaterThanOrEqual(count($etalon), count($actual));
+            foreach ($etalon as $key => $needle) {
+                Assertions::assertArrayHasKey($key, $actual);
+                Assertions::assertEquals($etalon[$key], $actual[$key]);
+            }
         }
     }