diff --git a/src/ExerciseRunner/CgiRunner.php b/src/ExerciseRunner/CgiRunner.php
index f6547f4f..3a8a41e7 100644
--- a/src/ExerciseRunner/CgiRunner.php
+++ b/src/ExerciseRunner/CgiRunner.php
@@ -217,7 +217,8 @@ private function getProcess(string $fileName, RequestInterface $request): Proces
             'SCRIPT_FILENAME' => $fileName,
             'REDIRECT_STATUS' => 302,
             'QUERY_STRING'    => $request->getUri()->getQuery(),
-            'REQUEST_URI'     => $request->getUri()->getPath()
+            'REQUEST_URI'     => $request->getUri()->getPath(),
+            'XDEBUG_MODE'     => 'off',
         ];
 
         $cgi = sprintf('php-cgi%s', DIRECTORY_SEPARATOR === '\\' ? '.exe' : '');
diff --git a/src/ExerciseRunner/CliRunner.php b/src/ExerciseRunner/CliRunner.php
index 3cf0736c..59f3e3aa 100644
--- a/src/ExerciseRunner/CliRunner.php
+++ b/src/ExerciseRunner/CliRunner.php
@@ -120,7 +120,7 @@ private function getPhpProcess(string $fileName, ArrayObject $args): Process
         return new Process(
             $args->prepend($fileName)->prepend(PHP_BINARY)->getArrayCopy(),
             dirname($fileName),
-            null,
+            ['XDEBUG_MODE' => 'off'],
             null,
             10
         );