diff --git a/test/Formatter/SignatureFormatterTest.php b/test/Formatter/SignatureFormatterTest.php
index <HASH>..<HASH> 100644
--- a/test/Formatter/SignatureFormatterTest.php
+++ b/test/Formatter/SignatureFormatterTest.php
@@ -13,6 +13,7 @@ namespace Psy\Test\Formatter;
 
 use Psy\Formatter\SignatureFormatter;
 use Psy\Reflection\ReflectionClassConstant;
+use Psy\Reflection\ReflectionConstant_;
 
 class SignatureFormatterTest extends \PHPUnit\Framework\TestCase
 {
@@ -68,6 +69,18 @@ class SignatureFormatterTest extends \PHPUnit\Framework\TestCase
                 new \ReflectionMethod('Psy\Test\Formatter\Fixtures\BoringTrait', 'boringMethod'),
                 'public function boringMethod($one = 1)',
             ],
+            [
+                new ReflectionConstant_('E_ERROR'),
+                'define("E_ERROR", 1)',
+            ],
+            [
+                new ReflectionConstant_('PHP_VERSION'),
+                'define("PHP_VERSION", "' . PHP_VERSION . '")',
+            ],
+            [
+                new ReflectionConstant_('__LINE__'),
+                'define("__LINE__", null)', // @todo show this as `unknown` in red or something?
+            ],
         ];
     }
Add test coverage for constant signature formatting.