diff --git a/composer.json b/composer.json
index 80c25442..1bb4ac25 100644
--- a/composer.json
+++ b/composer.json
@@ -27,7 +27,7 @@
         "mikehaertl/phpwkhtmltopdf": "^2.2",
         "monolog/monolog": "^1.21",
         "roave/security-advisories": "dev-master",
-        "symfony/console": "^4.0",
+        "symfony/console": "^4.0 <4.1.5",
         "symfony/filesystem": "^4.0",
         "symfony/process": "^4.0",
         "theorchard/monolog-cascade": "^0.4",
diff --git a/module/CLI/src/Command/Api/DisableKeyCommand.php b/module/CLI/src/Command/Api/DisableKeyCommand.php
index 386f838d..7d4c14c8 100644
--- a/module/CLI/src/Command/Api/DisableKeyCommand.php
+++ b/module/CLI/src/Command/Api/DisableKeyCommand.php
@@ -10,10 +10,11 @@ use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Style\SymfonyStyle;
 use Zend\I18n\Translator\TranslatorInterface;
+use function sprintf;
 
 class DisableKeyCommand extends Command
 {
-    const NAME = 'api-key:disable';
+    public const NAME = 'api-key:disable';
 
     /**
      * @var ApiKeyServiceInterface
@@ -31,14 +32,14 @@ class DisableKeyCommand extends Command
         parent::__construct();
     }
 
-    public function configure()
+    protected function configure(): void
     {
         $this->setName(self::NAME)
              ->setDescription($this->translator->translate('Disables an API key.'))
              ->addArgument('apiKey', InputArgument::REQUIRED, $this->translator->translate('The API key to disable'));
     }
 
-    public function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): void
     {
         $apiKey = $input->getArgument('apiKey');
         $io = new SymfonyStyle($input, $output);
diff --git a/module/CLI/src/Command/Api/GenerateKeyCommand.php b/module/CLI/src/Command/Api/GenerateKeyCommand.php
index 0b7fc476..0b6baafa 100644
--- a/module/CLI/src/Command/Api/GenerateKeyCommand.php
+++ b/module/CLI/src/Command/Api/GenerateKeyCommand.php
@@ -11,10 +11,11 @@ use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Style\SymfonyStyle;
 use Zend\I18n\Translator\TranslatorInterface;
+use function sprintf;
 
 class GenerateKeyCommand extends Command
 {
-    const NAME = 'api-key:generate';
+    public const NAME = 'api-key:generate';
 
     /**
      * @var ApiKeyServiceInterface
@@ -32,7 +33,7 @@ class GenerateKeyCommand extends Command
         parent::__construct();
     }
 
-    public function configure()
+    protected function configure(): void
     {
         $this->setName(self::NAME)
              ->setDescription($this->translator->translate('Generates a new valid API key.'))
@@ -44,7 +45,7 @@ class GenerateKeyCommand extends Command
              );
     }
 
-    public function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): void
     {
         $expirationDate = $input->getOption('expirationDate');
         $apiKey = $this->apiKeyService->create(isset($expirationDate) ? Chronos::parse($expirationDate) : null);
diff --git a/module/CLI/src/Command/Api/ListKeysCommand.php b/module/CLI/src/Command/Api/ListKeysCommand.php
index b67343d8..f3d4d30e 100644
--- a/module/CLI/src/Command/Api/ListKeysCommand.php
+++ b/module/CLI/src/Command/Api/ListKeysCommand.php
@@ -11,6 +11,8 @@ use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Style\SymfonyStyle;
 use Zend\I18n\Translator\TranslatorInterface;
+use function array_filter;
+use function sprintf;
 
 class ListKeysCommand extends Command
 {
@@ -36,7 +38,7 @@ class ListKeysCommand extends Command
         parent::__construct();
     }
 
-    public function configure()
+    protected function configure(): void
     {
         $this->setName(self::NAME)
              ->setDescription($this->translator->translate('Lists all the available API keys.'))
@@ -48,7 +50,7 @@ class ListKeysCommand extends Command
              );
     }
 
-    public function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): void
     {
         $io = new SymfonyStyle($input, $output);
         $enabledOnly = $input->getOption('enabledOnly');
@@ -62,16 +64,16 @@ class ListKeysCommand extends Command
             $messagePattern = $this->determineMessagePattern($row);
 
             // Set columns for this row
-            $rowData = [\sprintf($messagePattern, $key)];
+            $rowData = [sprintf($messagePattern, $key)];
             if (! $enabledOnly) {
-                $rowData[] = \sprintf($messagePattern, $this->getEnabledSymbol($row));
+                $rowData[] = sprintf($messagePattern, $this->getEnabledSymbol($row));
             }
             $rowData[] = $expiration !== null ? $expiration->toAtomString() : '-';
 
             $rows[] = $rowData;
         }
 
-        $io->table(\array_filter([
+        $io->table(array_filter([
             $this->translator->translate('Key'),
             ! $enabledOnly ? $this->translator->translate('Is enabled') : null,
             $this->translator->translate('Expiration date'),
diff --git a/module/CLI/src/Command/Config/GenerateCharsetCommand.php b/module/CLI/src/Command/Config/GenerateCharsetCommand.php
index c7287f7f..93b48541 100644
--- a/module/CLI/src/Command/Config/GenerateCharsetCommand.php
+++ b/module/CLI/src/Command/Config/GenerateCharsetCommand.php
@@ -9,10 +9,12 @@ use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Style\SymfonyStyle;
 use Zend\I18n\Translator\TranslatorInterface;
+use function sprintf;
+use function str_shuffle;
 
 class GenerateCharsetCommand extends Command
 {
-    const NAME = 'config:generate-charset';
+    public const NAME = 'config:generate-charset';
 
     /**
      * @var TranslatorInterface
@@ -25,20 +27,20 @@ class GenerateCharsetCommand extends Command
         parent::__construct();
     }
 
-    public function configure()
+    protected function configure(): void
     {
         $this->setName(self::NAME)
-             ->setDescription(\sprintf($this->translator->translate(
+             ->setDescription(sprintf($this->translator->translate(
                  'Generates a character set sample just by shuffling the default one, "%s". '
                  . 'Then it can be set in the SHORTCODE_CHARS environment variable'
              ), UrlShortener::DEFAULT_CHARS));
     }
 
-    public function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): void
     {
         $charSet = str_shuffle(UrlShortener::DEFAULT_CHARS);
         (new SymfonyStyle($input, $output))->success(
-            \sprintf($this->translator->translate('Character set: "%s"'), $charSet)
+            sprintf($this->translator->translate('Character set: "%s"'), $charSet)
         );
     }
 }
diff --git a/module/CLI/src/Command/Config/GenerateSecretCommand.php b/module/CLI/src/Command/Config/GenerateSecretCommand.php
index 684d6c8f..aaa7f2ef 100644
--- a/module/CLI/src/Command/Config/GenerateSecretCommand.php
+++ b/module/CLI/src/Command/Config/GenerateSecretCommand.php
@@ -9,12 +9,13 @@ use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Style\SymfonyStyle;
 use Zend\I18n\Translator\TranslatorInterface;
+use function sprintf;
 
 class GenerateSecretCommand extends Command
 {
     use StringUtilsTrait;
 
-    const NAME = 'config:generate-secret';
+    public const NAME = 'config:generate-secret';
 
     /**
      * @var TranslatorInterface
@@ -27,7 +28,7 @@ class GenerateSecretCommand extends Command
         parent::__construct();
     }
 
-    public function configure()
+    protected function configure(): void
     {
         $this->setName(self::NAME)
              ->setDescription($this->translator->translate(
@@ -35,7 +36,7 @@ class GenerateSecretCommand extends Command
              ));
     }
 
-    public function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): void
     {
         $secret = $this->generateRandomString(32);
         (new SymfonyStyle($input, $output))->success(
diff --git a/module/CLI/src/Command/Tag/CreateTagCommand.php b/module/CLI/src/Command/Tag/CreateTagCommand.php
index daf03d15..d50d2124 100644
--- a/module/CLI/src/Command/Tag/CreateTagCommand.php
+++ b/module/CLI/src/Command/Tag/CreateTagCommand.php
@@ -13,7 +13,7 @@ use Zend\I18n\Translator\TranslatorInterface;
 
 class CreateTagCommand extends Command
 {
-    const NAME = 'tag:create';
+    public const NAME = 'tag:create';
 
     /**
      * @var TagServiceInterface
@@ -31,7 +31,7 @@ class CreateTagCommand extends Command
         parent::__construct();
     }
 
-    protected function configure()
+    protected function configure(): void
     {
         $this
             ->setName(self::NAME)
@@ -44,7 +44,7 @@ class CreateTagCommand extends Command
             );
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): void
     {
         $io = new SymfonyStyle($input, $output);
         $tagNames = $input->getOption('name');
diff --git a/module/CLI/src/Command/Tag/DeleteTagsCommand.php b/module/CLI/src/Command/Tag/DeleteTagsCommand.php
index 5da57ede..0ea36e3f 100644
--- a/module/CLI/src/Command/Tag/DeleteTagsCommand.php
+++ b/module/CLI/src/Command/Tag/DeleteTagsCommand.php
@@ -13,7 +13,7 @@ use Zend\I18n\Translator\TranslatorInterface;
 
 class DeleteTagsCommand extends Command
 {
-    const NAME = 'tag:delete';
+    public const NAME = 'tag:delete';
 
     /**
      * @var TagServiceInterface
@@ -31,7 +31,7 @@ class DeleteTagsCommand extends Command
         parent::__construct();
     }
 
-    protected function configure()
+    protected function configure(): void
     {
         $this
             ->setName(self::NAME)
@@ -44,7 +44,7 @@ class DeleteTagsCommand extends Command
             );
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): void
     {
         $io = new SymfonyStyle($input, $output);
         $tagNames = $input->getOption('name');
diff --git a/module/CLI/src/Command/Tag/ListTagsCommand.php b/module/CLI/src/Command/Tag/ListTagsCommand.php
index ea860900..e82617dd 100644
--- a/module/CLI/src/Command/Tag/ListTagsCommand.php
+++ b/module/CLI/src/Command/Tag/ListTagsCommand.php
@@ -10,10 +10,11 @@ use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Style\SymfonyStyle;
 use Zend\I18n\Translator\TranslatorInterface;
+use function array_map;
 
 class ListTagsCommand extends Command
 {
-    const NAME = 'tag:list';
+    public const NAME = 'tag:list';
 
     /**
      * @var TagServiceInterface
@@ -31,14 +32,14 @@ class ListTagsCommand extends Command
         parent::__construct();
     }
 
-    protected function configure()
+    protected function configure(): void
     {
         $this
             ->setName(self::NAME)
             ->setDescription($this->translator->translate('Lists existing tags.'));
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): void
     {
         $io = new SymfonyStyle($input, $output);
         $io->table([$this->translator->translate('Name')], $this->getTagsRows());
@@ -51,7 +52,7 @@ class ListTagsCommand extends Command
             return [[$this->translator->translate('No tags yet')]];
         }
 
-        return \array_map(function (Tag $tag) {
+        return array_map(function (Tag $tag) {
             return [$tag->getName()];
         }, $tags);
     }
diff --git a/module/CLI/src/Command/Tag/RenameTagCommand.php b/module/CLI/src/Command/Tag/RenameTagCommand.php
index f76c05f2..e95affed 100644
--- a/module/CLI/src/Command/Tag/RenameTagCommand.php
+++ b/module/CLI/src/Command/Tag/RenameTagCommand.php
@@ -11,10 +11,11 @@ use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Style\SymfonyStyle;
 use Zend\I18n\Translator\TranslatorInterface;
+use function sprintf;
 
 class RenameTagCommand extends Command
 {
-    const NAME = 'tag:rename';
+    public const NAME = 'tag:rename';
 
     /**
      * @var TagServiceInterface
@@ -32,7 +33,7 @@ class RenameTagCommand extends Command
         parent::__construct();
     }
 
-    protected function configure()
+    protected function configure(): void
     {
         $this
             ->setName(self::NAME)
@@ -41,7 +42,7 @@ class RenameTagCommand extends Command
             ->addArgument('newName', InputArgument::REQUIRED, $this->translator->translate('New name of the tag.'));
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): void
     {
         $io = new SymfonyStyle($input, $output);
         $oldName = $input->getArgument('oldName');
@@ -51,7 +52,7 @@ class RenameTagCommand extends Command
             $this->tagService->renameTag($oldName, $newName);
             $io->success($this->translator->translate('Tag properly renamed.'));
         } catch (EntityDoesNotExistException $e) {
-            $io->error(\sprintf($this->translator->translate('A tag with name "%s" was not found'), $oldName));
+            $io->error(sprintf($this->translator->translate('A tag with name "%s" was not found'), $oldName));
         }
     }
 }
diff --git a/module/CLI/src/Command/Visit/ProcessVisitsCommand.php b/module/CLI/src/Command/Visit/ProcessVisitsCommand.php
index 2ae4e432..2a6980c9 100644
--- a/module/CLI/src/Command/Visit/ProcessVisitsCommand.php
+++ b/module/CLI/src/Command/Visit/ProcessVisitsCommand.php
@@ -13,6 +13,8 @@ use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Style\SymfonyStyle;
 use Zend\I18n\Translator\TranslatorInterface;
+use function sleep;
+use function sprintf;
 
 class ProcessVisitsCommand extends Command
 {
@@ -42,7 +44,7 @@ class ProcessVisitsCommand extends Command
         parent::__construct(null);
     }
 
-    public function configure()
+    protected function configure(): void
     {
         $this->setName(self::NAME)
              ->setDescription(
@@ -50,7 +52,7 @@ class ProcessVisitsCommand extends Command
              );
     }
 
-    public function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): void
     {
         $io = new SymfonyStyle($input, $output);
         $visits = $this->visitService->getUnlocatedVisits();
@@ -58,10 +60,10 @@ class ProcessVisitsCommand extends Command
         $count = 0;
         foreach ($visits as $visit) {
             $ipAddr = $visit->getRemoteAddr();
-            $io->write(\sprintf('%s <info>%s</info>', $this->translator->translate('Processing IP'), $ipAddr));
+            $io->write(sprintf('%s <info>%s</info>', $this->translator->translate('Processing IP'), $ipAddr));
             if ($ipAddr === IpAddress::LOCALHOST) {
                 $io->writeln(
-                    \sprintf(' (<comment>%s</comment>)', $this->translator->translate('Ignored localhost address'))
+                    sprintf(' (<comment>%s</comment>)', $this->translator->translate('Ignored localhost address'))
                 );
                 continue;
             }
@@ -75,13 +77,13 @@ class ProcessVisitsCommand extends Command
                 $visit->setVisitLocation($location);
                 $this->visitService->saveVisit($visit);
 
-                $io->writeln(\sprintf(
+                $io->writeln(sprintf(
                     ' (' . $this->translator->translate('Address located at "%s"') . ')',
                     $location->getCityName()
                 ));
             } catch (WrongIpException $e) {
                 $io->writeln(
-                    \sprintf(' <error>%s</error>', $this->translator->translate('An error occurred while locating IP'))
+                    sprintf(' <error>%s</error>', $this->translator->translate('An error occurred while locating IP'))
                 );
                 if ($io->isVerbose()) {
                     $this->getApplication()->renderException($e, $output);
@@ -91,11 +93,11 @@ class ProcessVisitsCommand extends Command
             if ($count === $this->ipLocationResolver->getApiLimit()) {
                 $count = 0;
                 $seconds = $this->ipLocationResolver->getApiInterval();
-                $io->note(\sprintf(
+                $io->note(sprintf(
                     $this->translator->translate('IP location resolver limit reached. Waiting %s seconds...'),
                     $seconds
                 ));
-                \sleep($seconds);
+                sleep($seconds);
             }
         }