diff --git a/src/Preg.php b/src/Preg.php
index 400abbf..98b4d29 100644
--- a/src/Preg.php
+++ b/src/Preg.php
@@ -395,7 +395,7 @@ private static function checkSetOrder(int $flags): void
      * @return array<int|string, string>
      * @throws UnexpectedNullMatchException
      */
-    private static function enforceNonNullMatches(string $pattern, array $matches, string $variantMethod)
+    private static function enforceNonNullMatches(string $pattern, array $matches, string $variantMethod): array
     {
         foreach ($matches as $group => $match) {
             if (is_string($match) || (is_array($match) && is_string($match[0]))) {
@@ -414,7 +414,7 @@ private static function enforceNonNullMatches(string $pattern, array $matches, s
      * @return array<int|string, list<string>>
      * @throws UnexpectedNullMatchException
      */
-    private static function enforceNonNullMatchAll(string $pattern, array $matches, string $variantMethod)
+    private static function enforceNonNullMatchAll(string $pattern, array $matches, string $variantMethod): array
     {
         foreach ($matches as $group => $groupMatches) {
             foreach ($groupMatches as $match) {