diff --git a/src/Psalm/Config/FileFilter.php b/src/Psalm/Config/FileFilter.php
index 2d3187e7462..74b9d25c914 100644
--- a/src/Psalm/Config/FileFilter.php
+++ b/src/Psalm/Config/FileFilter.php
@@ -434,7 +434,7 @@ public static function loadFromXMLElement(
     private static function isRegularExpression(string $string): bool
     {
         set_error_handler(
-            static fn(): bool => false,
+            static fn(): bool => true,
             E_WARNING
         );
         $is_regexp = preg_match($string, '') !== false;