diff --git a/src/Symfony/Component/HttpFoundation/HeaderUtils.php b/src/Symfony/Component/HttpFoundation/HeaderUtils.php
index f91c7e1d97d8..3456edace0dc 100644
--- a/src/Symfony/Component/HttpFoundation/HeaderUtils.php
+++ b/src/Symfony/Component/HttpFoundation/HeaderUtils.php
@@ -256,7 +256,7 @@ public static function parseQuery(string $query, bool $ignoreBrackets = false, s
     private static function groupParts(array $matches, string $separators, bool $first = true): array
     {
         $separator = $separators[0];
-        $separators = substr($separators, 1);
+        $separators = substr($separators, 1) ?: '';
         $i = 0;
 
         if ('' === $separators && !$first) {