diff --git a/README.md b/README.md
index b1eaaf0..0ca6b94 100644
--- a/README.md
+++ b/README.md
@@ -51,7 +51,7 @@ Not shown: the normal test summary output you're used to seeing at the end of a
 ## Requirements
 
 * PHP 5.6 or newer.
-* [PHPUnit][PHPUnit] 5.5 or newer. PHPUnit 6 not yet supported.
+* [PHPUnit][PHPUnit] 5.5 or newer.
 
 ## Testing
 
diff --git a/composer.json b/composer.json
index ad7eaa8..e2f5802 100644
--- a/composer.json
+++ b/composer.json
@@ -8,7 +8,7 @@
     }
   ],
   "require": {
-    "phpunit/phpunit": "^5.5"
+    "phpunit/phpunit": "^5.5|^6"
   },
   "autoload": {
     "psr-4": {
diff --git a/src/ImmediateExceptionPrinter.php b/src/ImmediateExceptionPrinter.php
index 1466b50..049a8ad 100644
--- a/src/ImmediateExceptionPrinter.php
+++ b/src/ImmediateExceptionPrinter.php
@@ -1,147 +1,12 @@
 <?php
 namespace ScriptFUSION\PHPUnitImmediateExceptionPrinter;
 
-class ImmediateExceptionPrinter extends \PHPUnit_TextUI_ResultPrinter
-{
-    /**
-     * The exception thrown by the last test.
-     *
-     * @var \Exception|null
-     */
-    protected $exception;
-
-    /**
-     * PHPUnit built-in progress indication character, e.g. E for error.
-     *
-     * @var string
-     */
-    protected $progress;
-
-    /**
-     * Last colour used by a progress indicator.
-     *
-     * @var string
-     */
-    protected $lastColour;
-
-    private static $performanceThresholds = [
-        'fg-red' => 1000,
-        'fg-yellow' => 200,
-        'fg-green' => 0,
-    ];
-
-    public function startTest(\PHPUnit_Framework_Test $test)
-    {
-        parent::startTest($test);
-
-        $this->exception = $this->progress = null;
-        $this->lastColour = 'fg-green,bold';
-    }
-
-    protected function writeProgress($progress)
+if (class_exists(\PHPUnit_TextUI_ResultPrinter::class)) {
+    class ImmediateExceptionPrinter extends PhpUnit5Printer
     {
-        // Record progress so it can be written later instead of at start of line.
-        $this->progress = $progress;
-
-        ++$this->numTestsRun;
     }
-
-    protected function writeProgressWithColor($color, $buffer)
-    {
-        parent::writeProgressWithColor($color, $buffer);
-
-        $this->lastColour = $color;
-    }
-
-    public function endTest(\PHPUnit_Framework_Test $test, $time)
-    {
-        parent::endTest($test, $time);
-
-        $this->write(sprintf(
-            '%3d%% %s ',
-            floor($this->numTestsRun / $this->numTests * 100),
-            $this->progress
-        ));
-        $this->writeWithColor($this->lastColour, \PHPUnit_Util_Test::describe($test), false);
-        $this->writePerformance($time);
-
-        if ($this->exception) {
-            $this->printExceptionTrace($this->exception);
-        }
-    }
-
-    /**
-     * Writes the test performance metric formatted as the number of milliseconds elapsed.
-     *
-     * @param float $time Number of seconds elapsed.
-     */
-    protected function writePerformance($time)
+} else {
+    class ImmediateExceptionPrinter extends PhpUnit6Printer
     {
-        $ms = round($time * 1000);
-
-        foreach (self::$performanceThresholds as $colour => $threshold) {
-            if ($ms > $threshold) {
-                break;
-            }
-        }
-
-        $this->writeWithColor($colour, " ($ms ms)");
-    }
-
-    protected function printExceptionTrace(\Exception $exception)
-    {
-        $this->writeNewLine();
-
-        // Parse nested exception trace line by line.
-        foreach (explode("\n", $exception) as $line) {
-            // Print exception name and message.
-            if (!$exception instanceof \PHPUnit_Framework_AssertionFailedError
-                && false !== $pos = strpos($line, ': ')
-            ) {
-                $whitespace = str_repeat(' ', $pos + 2);
-                $this->writeWithColor('bg-red,fg-white', $whitespace);
-
-                // Exception name.
-                $this->writeWithColor('bg-red,fg-white', sprintf(' %s ', substr($line, 0, $pos)), false);
-                // Exception message.
-                $this->writeWithColor('fg-red', substr($line, $pos + 1));
-
-                $this->writeWithColor('bg-red,fg-white', $whitespace);
-
-                continue;
-            }
-
-            $this->writeWithColor('fg-red', $line);
-        }
-    }
-
-    /**
-     * Called when an exception is thrown in the test runner.
-     *
-     * @param \PHPUnit_Framework_Test $test
-     * @param \Exception $e
-     * @param float $time
-     */
-    public function addError(\PHPUnit_Framework_Test $test, \Exception $e, $time)
-    {
-        $this->writeProgressWithColor('fg-red,bold', 'E');
-
-        $this->exception = $e;
-        $this->lastTestFailed = true;
-    }
-
-    /**
-     * Called when an assertion fails in the test runner.
-     *
-     * @param \PHPUnit_Framework_Test $test
-     * @param \PHPUnit_Framework_AssertionFailedError $e
-     * @param float $time
-     */
-    public function addFailure(\PHPUnit_Framework_Test $test, \PHPUnit_Framework_AssertionFailedError $e, $time)
-    {
-        $this->writeProgressWithColor('fg-red,bold', 'F');
-
-        $this->exception = $e;
-        $this->lastTestFailed = true;
     }
 }
diff --git a/src/PhpUnit5Printer.php b/src/PhpUnit5Printer.php
new file mode 100644
index 0000000..3738560
--- /dev/null
+++ b/src/PhpUnit5Printer.php
@@ -0,0 +1,38 @@
+<?php
+namespace ScriptFUSION\PHPUnitImmediateExceptionPrinter;
+
+class PhpUnit5Printer extends \PHPUnit_TextUI_ResultPrinter
+{
+    use Printer;
+
+    public function startTest(\PHPUnit_Framework_Test $test)
+    {
+        parent::startTest($test);
+
+        $this->onStartTest();
+    }
+
+    protected function writeProgressWithColor($color, $buffer)
+    {
+        parent::writeProgressWithColor($color, $buffer);
+
+        $this->onWriteProgressWithColor($color);
+    }
+
+    public function endTest(\PHPUnit_Framework_Test $test, $time)
+    {
+        parent::endTest($test, $time);
+
+        $this->onEndTest($test, $time);
+    }
+
+    public function addError(\PHPUnit_Framework_Test $test, \Exception $e, $time)
+    {
+        $this->onAddError($e);
+    }
+
+    public function addFailure(\PHPUnit_Framework_Test $test, \PHPUnit_Framework_AssertionFailedError $e, $time)
+    {
+        $this->onAddFailure($e);
+    }
+}
diff --git a/src/PhpUnit6Printer.php b/src/PhpUnit6Printer.php
new file mode 100644
index 0000000..adc427b
--- /dev/null
+++ b/src/PhpUnit6Printer.php
@@ -0,0 +1,42 @@
+<?php
+namespace ScriptFUSION\PHPUnitImmediateExceptionPrinter;
+
+use PHPUnit\Framework\AssertionFailedError;
+use PHPUnit\Framework\Test;
+use PHPUnit\TextUI\ResultPrinter;
+
+class PhpUnit6Printer extends ResultPrinter
+{
+    use Printer;
+
+    public function startTest(Test $test)
+    {
+        parent::startTest($test);
+
+        $this->onStartTest();
+    }
+
+    protected function writeProgressWithColor($color, $buffer)
+    {
+        parent::writeProgressWithColor($color, $buffer);
+
+        $this->onWriteProgressWithColor($color);
+    }
+
+    public function endTest(Test $test, $time)
+    {
+        parent::endTest($test, $time);
+
+        $this->onEndTest($test, $time);
+    }
+
+    public function addError(Test $test, \Exception $e, $time)
+    {
+        $this->onAddError($e);
+    }
+
+    public function addFailure(Test $test, AssertionFailedError $e, $time)
+    {
+        $this->onAddFailure($e);
+    }
+}
diff --git a/src/Printer.php b/src/Printer.php
new file mode 100644
index 0000000..9108c80
--- /dev/null
+++ b/src/Printer.php
@@ -0,0 +1,174 @@
+<?php
+namespace ScriptFUSION\PHPUnitImmediateExceptionPrinter;
+
+use PHPUnit\Framework\AssertionFailedError;
+use PHPUnit\Framework\Test;
+
+trait Printer
+{
+    /**
+     * The exception thrown by the last test.
+     *
+     * @var \Exception|null
+     */
+    protected $exception;
+
+    /**
+     * PHPUnit built-in progress indication character, e.g. E for error.
+     *
+     * @var string
+     */
+    protected $progress;
+
+    /**
+     * Last colour used by a progress indicator.
+     *
+     * @var string
+     */
+    protected $lastColour;
+
+    private static $performanceThresholds = [
+        'fg-red' => 1000,
+        'fg-yellow' => 200,
+        'fg-green' => 0,
+    ];
+
+    /**
+     * Invoked when a test starts.
+     */
+    protected function onStartTest()
+    {
+        $this->exception = $this->progress = null;
+        $this->lastColour = 'fg-green,bold';
+    }
+
+    /**
+     * Writes progress to the output buffer.
+     *
+     * @param string $progress
+     */
+    protected function writeProgress($progress)
+    {
+        // Record progress so it can be written later instead of at start of line.
+        $this->progress = $progress;
+
+        ++$this->numTestsRun;
+    }
+
+    /**
+     * Invoked when coloured progress text is written.
+     *
+     * @param string $color PHPUnit colour name.
+     */
+    protected function onWriteProgressWithColor($color)
+    {
+        $this->lastColour = $color;
+    }
+
+    /**
+     * Invoked when a test ends.
+     *
+     * @param Test $test
+     * @param float $time Number of seconds elapsed.
+     */
+    protected function onEndTest($test, $time)
+    {
+        $this->write(sprintf(
+            '%3d%% %s ',
+            floor($this->numTestsRun / $this->numTests * 100),
+            $this->progress
+        ));
+        $this->writeWithColor($this->lastColour, $this->describeTest($test), false);
+        $this->writePerformance($time);
+
+        if ($this->exception) {
+            $this->writeExceptionTrace($this->exception);
+        }
+    }
+
+    protected function describeTest($test)
+    {
+        if (class_exists(\PHPUnit_Util_Test::class)) {
+            return \PHPUnit_Util_Test::describe($test);
+        }
+
+        return \PHPUnit\Util\Test::describe($test);
+    }
+
+    /**
+     * Writes the test performance metric formatted as the number of milliseconds elapsed.
+     *
+     * @param float $time Number of seconds elapsed.
+     */
+    protected function writePerformance($time)
+    {
+        $ms = round($time * 1000);
+
+        foreach (self::$performanceThresholds as $colour => $threshold) {
+            if ($ms > $threshold) {
+                break;
+            }
+        }
+
+        $this->writeWithColor($colour, " ($ms ms)");
+    }
+
+    /**
+     * Writes the specified exception to the output buffer.
+     *
+     * @param \Exception $exception Exception.
+     */
+    protected function writeExceptionTrace(\Exception $exception)
+    {
+        $this->writeNewLine();
+
+        // Parse nested exception trace line by line.
+        foreach (explode("\n", $exception) as $line) {
+            // Print exception name and message.
+            if (!$exception instanceof \PHPUnit_Framework_AssertionFailedError
+                && !$exception instanceof AssertionFailedError
+                && false !== $pos = strpos($line, ': ')
+            ) {
+                $whitespace = str_repeat(' ', $pos + 2);
+                $this->writeWithColor('bg-red,fg-white', $whitespace);
+
+                // Exception name.
+                $this->writeWithColor('bg-red,fg-white', sprintf(' %s ', substr($line, 0, $pos)), false);
+                // Exception message.
+                $this->writeWithColor('fg-red', substr($line, $pos + 1));
+
+                $this->writeWithColor('bg-red,fg-white', $whitespace);
+
+                continue;
+            }
+
+            $this->writeWithColor('fg-red', $line);
+        }
+    }
+
+    /**
+     * Invoked when an exception is thrown in the test runner.
+     *
+     * @param \Exception $e
+     */
+    protected function onAddError(\Exception $e)
+    {
+        $this->writeProgressWithColor('fg-red,bold', 'E');
+
+        $this->exception = $e;
+        $this->lastTestFailed = true;
+    }
+
+    /**
+     * Invoked when an assertion fails in the test runner.
+     *
+     * @param AssertionFailedError $e
+     */
+    protected function onAddFailure($e)
+    {
+        $this->writeProgressWithColor('fg-red,bold', 'F');
+
+        $this->exception = $e;
+        $this->lastTestFailed = true;
+    }
+}
diff --git a/test/CapabilitiesTest.php b/test/CapabilitiesTest.php
index 4429098..68baa09 100644
--- a/test/CapabilitiesTest.php
+++ b/test/CapabilitiesTest.php
@@ -1,7 +1,9 @@
 <?php
 namespace ScriptFUSIONTest\PHPUnitImmediateExceptionPrinter;
 
-final class CapabilitiesTest extends \PHPUnit_Framework_TestCase
+use PHPUnit\Framework\TestCase;
+
+final class CapabilitiesTest extends TestCase
 {
     public function testSuccess()
     {
@@ -30,7 +32,7 @@ public function testDiffFailure()
 
     public function testSkipped()
     {
-        $this->markTestSkipped();
+        self::markTestSkipped();
     }
 
     public function testRisky()
@@ -39,7 +41,7 @@ public function testRisky()
 
     public function testIncomplete()
     {
-        $this->markTestIncomplete();
+        self::markTestIncomplete();
     }
 
     /**
diff --git a/test/functional/PHPUnit runner.php b/test/functional/PHPUnit runner.php
index 36f48eb..a56bb0f 100644
--- a/test/functional/PHPUnit runner.php	
+++ b/test/functional/PHPUnit runner.php	
@@ -1,4 +1,8 @@
 <?php
 require_once 'vendor/autoload.php';
 
-PHPUnit_TextUI_Command::main();
+if (class_exists(PHPUnit_TextUI_Command::class)) {
+    PHPUnit_TextUI_Command::main();
+} else {
+    PHPUnit\TextUI\Command::main();
+}