diff --git a/src/Util/XDebugFilterScriptGenerator.php b/src/Util/XDebugFilterScriptGenerator.php
index 2879f0b2334..6c0ac9dc318 100644
--- a/src/Util/XDebugFilterScriptGenerator.php
+++ b/src/Util/XDebugFilterScriptGenerator.php
@@ -21,14 +21,14 @@ public function generate(array $filterData, array $whitelistedFiles): string
         $files = \implode(",\n", $files);
 
         return <<<EOF
-<?php
+<?php declare(strict_types=1);
 if (!\\function_exists('xdebug_set_filter')) {
     return;
 }
 
-xdebug_set_filter(
-    XDEBUG_FILTER_CODE_COVERAGE,
-    XDEBUG_PATH_WHITELIST,
+\\xdebug_set_filter(
+    \\XDEBUG_FILTER_CODE_COVERAGE,
+    \\XDEBUG_PATH_WHITELIST,
     [
 $files
     ]
diff --git a/tests/end-to-end/dump-xdebug-filter.phpt b/tests/end-to-end/dump-xdebug-filter.phpt
index 23b69fe0d43..50a6c8196da 100644
--- a/tests/end-to-end/dump-xdebug-filter.phpt
+++ b/tests/end-to-end/dump-xdebug-filter.phpt
@@ -16,14 +16,14 @@ require __DIR__ . '/../bootstrap.php';
 PHPUnit\TextUI\Command::main();
 --EXPECTF--
 PHPUnit %s by Sebastian Bergmann and contributors.
-<?php
+<?php declare(strict_types=1);
 if (!\function_exists('xdebug_set_filter')) {
     return;
 }
 
-xdebug_set_filter(
-    XDEBUG_FILTER_CODE_COVERAGE,
-    XDEBUG_PATH_WHITELIST,
+\xdebug_set_filter(
+    \XDEBUG_FILTER_CODE_COVERAGE,
+    \XDEBUG_PATH_WHITELIST,
     [
         %s
     ]
diff --git a/tests/unit/Util/_files/expectedXDebugFilterScript.txt b/tests/unit/Util/_files/expectedXDebugFilterScript.txt
index b3e8599f304..dfcf8060b1f 100644
--- a/tests/unit/Util/_files/expectedXDebugFilterScript.txt
+++ b/tests/unit/Util/_files/expectedXDebugFilterScript.txt
@@ -1,11 +1,11 @@
-<?php
+<?php declare(strict_types=1);
 if (!\function_exists('xdebug_set_filter')) {
     return;
 }
 
-xdebug_set_filter(
-    XDEBUG_FILTER_CODE_COVERAGE,
-    XDEBUG_PATH_WHITELIST,
+\xdebug_set_filter(
+    \XDEBUG_FILTER_CODE_COVERAGE,
+    \XDEBUG_PATH_WHITELIST,
     [
         'src/somePath',
         'src/foo.php',