diff --git a/core/functions/session_proxy.php b/core/functions/session_proxy.php
index 67434c8139..14b16d9a53 100644
--- a/core/functions/session_proxy.php
+++ b/core/functions/session_proxy.php
@@ -57,7 +57,10 @@ public static function init(): void
         self::migrateLegacySessionIfNeeded($store);
 
         // Start PHP session with cookies disabled (Laravel owns the cookie).
-        if (session_status() === PHP_SESSION_NONE) {
+        // Skipped on CLI: there are no headers to send there, and the merge
+        // below fills $_SESSION either way. The CLI installer reaches this
+        // after it has printed, so each call would only warn.
+        if (PHP_SAPI !== 'cli' && session_status() === PHP_SESSION_NONE) {
             ini_set('session.use_cookies', '0');
             if (!defined('PHP_VERSION_ID') || PHP_VERSION_ID < 80400) {
                 ini_set('session.use_only_cookies', '0');
diff --git a/index.php b/index.php
index 7a9ec39ecd..acf3a7f105 100644
--- a/index.php
+++ b/index.php
@@ -82,7 +82,9 @@
 if (IN_INSTALL_MODE) {
     // Set some settings, and address some IE issues.
     @ini_set('url_rewriter.tags', '');
-    if (session_status() === PHP_SESSION_NONE) {
+    // Browser-only session tweaks. The CLI installer includes this file after
+    // it has already printed, so on CLI these only warn about sent headers.
+    if (PHP_SAPI !== 'cli' && session_status() === PHP_SESSION_NONE) {
         ini_set('session.use_trans_sid', 0);
         ini_set('session.use_only_cookies', 1);
     }