diff --git a/composer/Plugin/Scaffold/ComposerScaffoldCommand.php b/composer/Plugin/Scaffold/ComposerScaffoldCommand.php
index 6de8aa4bf8f..c1b34ca503b 100644
--- a/composer/Plugin/Scaffold/ComposerScaffoldCommand.php
+++ b/composer/Plugin/Scaffold/ComposerScaffoldCommand.php
@@ -47,7 +47,7 @@ EOT
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     $handler = new Handler($this->getComposer(), $this->getIO());
     $handler->scaffold();
     return 0;
diff --git a/core/lib/Drupal/Core/Command/DbDumpCommand.php b/core/lib/Drupal/Core/Command/DbDumpCommand.php
index a36366cc2eb..c1b46728954 100644
--- a/core/lib/Drupal/Core/Command/DbDumpCommand.php
+++ b/core/lib/Drupal/Core/Command/DbDumpCommand.php
@@ -48,7 +48,7 @@ class DbDumpCommand extends DbCommandBase {
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     $connection = $this->getDatabaseConnection($input);
 
     // If not explicitly set, disable ANSI which will break generated php.
diff --git a/core/lib/Drupal/Core/Command/DbImportCommand.php b/core/lib/Drupal/Core/Command/DbImportCommand.php
index 4765692168f..cf461df7346 100644
--- a/core/lib/Drupal/Core/Command/DbImportCommand.php
+++ b/core/lib/Drupal/Core/Command/DbImportCommand.php
@@ -32,7 +32,7 @@ class DbImportCommand extends DbCommandBase {
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     $script = $input->getArgument('script');
     if (!is_file($script)) {
       $output->writeln('File must exist.');
diff --git a/core/lib/Drupal/Core/Command/GenerateProxyClassCommand.php b/core/lib/Drupal/Core/Command/GenerateProxyClassCommand.php
index ac99bc6c3a4..0dc481c6359 100644
--- a/core/lib/Drupal/Core/Command/GenerateProxyClassCommand.php
+++ b/core/lib/Drupal/Core/Command/GenerateProxyClassCommand.php
@@ -50,7 +50,7 @@ class GenerateProxyClassCommand extends Command {
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     $class_name = ltrim($input->getArgument('class_name'), '\\');
     $namespace_root = $input->getArgument('namespace_root_path');
 
diff --git a/core/lib/Drupal/Core/Command/GenerateTheme.php b/core/lib/Drupal/Core/Command/GenerateTheme.php
index fbfebbf2d17..9da8af0386d 100644
--- a/core/lib/Drupal/Core/Command/GenerateTheme.php
+++ b/core/lib/Drupal/Core/Command/GenerateTheme.php
@@ -51,7 +51,7 @@ class GenerateTheme extends Command {
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     $io = new SymfonyStyle($input, $output);
 
     // Change the directory to the Drupal root.
diff --git a/core/lib/Drupal/Core/Command/InstallCommand.php b/core/lib/Drupal/Core/Command/InstallCommand.php
index 4b76025c11d..2e73df37962 100644
--- a/core/lib/Drupal/Core/Command/InstallCommand.php
+++ b/core/lib/Drupal/Core/Command/InstallCommand.php
@@ -60,7 +60,7 @@ class InstallCommand extends Command {
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     $io = new SymfonyStyle($input, $output);
     if (!extension_loaded('pdo_sqlite')) {
       $io->getErrorStyle()->error('You must have the pdo_sqlite PHP extension installed. See core/INSTALL.sqlite.txt for instructions.');
diff --git a/core/lib/Drupal/Core/Command/QuickStartCommand.php b/core/lib/Drupal/Core/Command/QuickStartCommand.php
index 690b20eb3b2..572f6415c20 100644
--- a/core/lib/Drupal/Core/Command/QuickStartCommand.php
+++ b/core/lib/Drupal/Core/Command/QuickStartCommand.php
@@ -44,7 +44,7 @@ class QuickStartCommand extends Command {
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     $command = $this->getApplication()->find('install');
 
     $arguments = [
diff --git a/core/lib/Drupal/Core/Command/ServerCommand.php b/core/lib/Drupal/Core/Command/ServerCommand.php
index 6c153241b2d..09559db2aaf 100644
--- a/core/lib/Drupal/Core/Command/ServerCommand.php
+++ b/core/lib/Drupal/Core/Command/ServerCommand.php
@@ -58,7 +58,7 @@ class ServerCommand extends Command {
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     $io = new SymfonyStyle($input, $output);
 
     $host = $input->getOption('host');
diff --git a/core/modules/system/tests/src/Kernel/Scripts/DbCommandBaseTest.php b/core/modules/system/tests/src/Kernel/Scripts/DbCommandBaseTest.php
index cef2414ec00..5f29d4ed3f6 100644
--- a/core/modules/system/tests/src/Kernel/Scripts/DbCommandBaseTest.php
+++ b/core/modules/system/tests/src/Kernel/Scripts/DbCommandBaseTest.php
@@ -129,7 +129,7 @@ class DbCommandBaseTester extends DbCommandBase {
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     // Empty implementation for testing.
     return 0;
   }
diff --git a/core/tests/Drupal/TestSite/Commands/TestSiteInstallCommand.php b/core/tests/Drupal/TestSite/Commands/TestSiteInstallCommand.php
index fb92ee8ec1b..e9d4349483a 100644
--- a/core/tests/Drupal/TestSite/Commands/TestSiteInstallCommand.php
+++ b/core/tests/Drupal/TestSite/Commands/TestSiteInstallCommand.php
@@ -81,7 +81,7 @@ class TestSiteInstallCommand extends Command {
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     // Determines and validates the setup class prior to installing a database
     // to avoid creating unnecessary sites.
     $root = dirname(__DIR__, 5);
diff --git a/core/tests/Drupal/TestSite/Commands/TestSiteReleaseLocksCommand.php b/core/tests/Drupal/TestSite/Commands/TestSiteReleaseLocksCommand.php
index d0378779642..c88abb84ab1 100644
--- a/core/tests/Drupal/TestSite/Commands/TestSiteReleaseLocksCommand.php
+++ b/core/tests/Drupal/TestSite/Commands/TestSiteReleaseLocksCommand.php
@@ -29,7 +29,7 @@ class TestSiteReleaseLocksCommand extends Command {
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     TestDatabase::releaseAllTestLocks();
     $output->writeln('<info>Successfully released all the test database locks</info>');
     return 0;
diff --git a/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php b/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php
index 0eff01cedf1..a2b5f54e320 100644
--- a/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php
+++ b/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php
@@ -37,7 +37,7 @@ class TestSiteTearDownCommand extends Command {
   /**
    * {@inheritdoc}
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     $db_prefix = $input->getArgument('db-prefix');
     // Validate the db_prefix argument.
     try {
diff --git a/core/tests/Drupal/TestSite/Commands/TestSiteUserLoginCommand.php b/core/tests/Drupal/TestSite/Commands/TestSiteUserLoginCommand.php
index cb8c119d5af..6ea3395ea53 100644
--- a/core/tests/Drupal/TestSite/Commands/TestSiteUserLoginCommand.php
+++ b/core/tests/Drupal/TestSite/Commands/TestSiteUserLoginCommand.php
@@ -41,7 +41,7 @@ class TestSiteUserLoginCommand extends Command {
    *
    * @throws \Symfony\Component\Console\Exception\InvalidArgumentException
    */
-  protected function execute(InputInterface $input, OutputInterface $output) {
+  protected function execute(InputInterface $input, OutputInterface $output): int {
     $root = dirname(__DIR__, 5);
     chdir($root);