diff --git a/.github/nightly_matrix.php b/.github/nightly_matrix.php
index f0603dd97d7..68bc8a3ee1c 100644
--- a/.github/nightly_matrix.php
+++ b/.github/nightly_matrix.php
@@ -101,7 +101,7 @@ function get_macos_matrix_include(array $branches) {
                     'branch' => $branch,
                     'debug' => $debug,
                     'zts' => $zts,
-                    'os' => $branch['name'] === 'master' ? '13' : '12',
+                    'os' => '13',
                     'arch' => 'X64',
                     'test_jit' => true,
                 ];