diff --git a/src/Runner/Phpt/TestCase.php b/src/Runner/Phpt/TestCase.php
index 5d2bafe2f14..308b42a3e0b 100644
--- a/src/Runner/Phpt/TestCase.php
+++ b/src/Runner/Phpt/TestCase.php
@@ -350,23 +350,7 @@ private function shouldTestBeSkipped(array $sections, array $settings): bool
             $output = $this->runCodeInLocalSandbox($skipIfCode);
         }
 
-        if (str_contains($output, 'Parse error:')) {
-            EventFacade::emitter()->testRunnerTriggeredPhpunitWarning(
-                sprintf(
-                    'SKIPIF section triggered a parse error: %s',
-                    $output,
-                ),
-            );
-        }
-
-        if (str_contains($output, 'Fatal error:')) {
-            EventFacade::emitter()->testRunnerTriggeredPhpunitWarning(
-                sprintf(
-                    'SKIPIF section triggered a fatal error: %s',
-                    $output,
-                ),
-            );
-        }
+        $this->triggerRunnerWarningOnPhpErrors('SKIPIF', $output);
 
         if (strncasecmp('skip', ltrim($output), 4) === 0) {
             $message = '';
@@ -448,19 +432,21 @@ private function runClean(array $sections, bool $collectCoverage): void
         $cleanCode = (new Renderer)->render($this->filename, $sections['CLEAN']);
 
         if ($this->shouldRunInSubprocess($sections, $cleanCode)) {
-            $result = JobRunnerRegistry::run(
+            $jobResult = JobRunnerRegistry::run(
                 new Job(
                     $cleanCode,
                     $this->settings($collectCoverage),
                 ),
             );
 
-            EventFacade::emitter()->childProcessFinished($result->stdout(), $result->stderr());
+            $output = $jobResult->stdout();
 
-            return;
+            EventFacade::emitter()->childProcessFinished($jobResult->stdout(), $jobResult->stderr());
+        } else {
+            $output = $this->runCodeInLocalSandbox($cleanCode);
         }
 
-        $this->runCodeInLocalSandbox($cleanCode);
+        $this->triggerRunnerWarningOnPhpErrors('CLEAN', $output);
     }
 
     /**
@@ -698,4 +684,27 @@ private function settings(bool $collectCoverage): array
 
         return $settings;
     }
+
+    private function triggerRunnerWarningOnPhpErrors(string $section, string $output): void
+    {
+        if (str_contains($output, 'Parse error:')) {
+            EventFacade::emitter()->testRunnerTriggeredPhpunitWarning(
+                sprintf(
+                    '%s section triggered a parse error: %s',
+                    $section,
+                    $output,
+                ),
+            );
+        }
+
+        if (str_contains($output, 'Fatal error:')) {
+            EventFacade::emitter()->testRunnerTriggeredPhpunitWarning(
+                sprintf(
+                    '%s section triggered a fatal error: %s',
+                    $section,
+                    $output,
+                ),
+            );
+        }
+    }
 }
diff --git a/tests/end-to-end/_files/phpt-clean-parse-error.phpt b/tests/end-to-end/_files/phpt-clean-parse-error.phpt
new file mode 100644
index 00000000000..d9d370b1735
--- /dev/null
+++ b/tests/end-to-end/_files/phpt-clean-parse-error.phpt
@@ -0,0 +1,11 @@
+--TEST--
+https://github.com/sebastianbergmann/phpunit/issues/5991
+--CLEAN--
+<?php
+if (rand(0,1)) // intentional PHP Parse error (missing opening curly brace)
+}
+--FILE--
+<?php declare(strict_types=1);
+echo 'hello world';
+--EXPECTF--
+hello world
diff --git a/tests/end-to-end/phpt/phpt-clean-parse-error.phpt b/tests/end-to-end/phpt/phpt-clean-parse-error.phpt
new file mode 100644
index 00000000000..6ec33994151
--- /dev/null
+++ b/tests/end-to-end/phpt/phpt-clean-parse-error.phpt
@@ -0,0 +1,28 @@
+--TEST--
+https://github.com/sebastianbergmann/phpunit/issues/5991
+--FILE--
+<?php declare(strict_types=1);
+$_SERVER['argv'][] = '--do-not-cache-result';
+$_SERVER['argv'][] = '--no-configuration';
+$_SERVER['argv'][] = __DIR__ . '/../_files/phpt-clean-parse-error.phpt';
+
+require_once __DIR__ . '/../../bootstrap.php';
+
+(new PHPUnit\TextUI\Application)->run($_SERVER['argv']);
+--EXPECTF--
+PHPUnit %s by Sebastian Bergmann and contributors.
+
+Runtime: %s
+
+.                                                                   1 / 1 (100%)
+
+Time: %s, Memory: %s
+
+There was 1 PHPUnit test runner warning:
+
+1) CLEAN section triggered a parse error: 
+Parse error: Unmatched '}' in Standard input code on line 3
+
+
+OK, but there were issues!
+Tests: 1, Assertions: 1, PHPUnit Warnings: 1.