diff --git a/typo3/sysext/backend/Classes/Middleware/OutputCompression.php b/typo3/sysext/backend/Classes/Middleware/OutputCompression.php
index 6bb93af85409..5e2cb0c24097 100644
--- a/typo3/sysext/backend/Classes/Middleware/OutputCompression.php
+++ b/typo3/sysext/backend/Classes/Middleware/OutputCompression.php
@@ -52,7 +52,7 @@ protected function initializeOutputCompression()
     {
         if (extension_loaded('zlib') && $GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel']) {
             if (MathUtility::canBeInterpretedAsInteger($GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel'])) {
-                @ini_set('zlib.output_compression_level', $GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel']);
+                @ini_set('zlib.output_compression_level', (string)$GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel']);
             }
             ob_start('ob_gzhandler');
         }
diff --git a/typo3/sysext/core/Classes/Core/Bootstrap.php b/typo3/sysext/core/Classes/Core/Bootstrap.php
index 6c43efebff48..ddad790ed7a9 100644
--- a/typo3/sysext/core/Classes/Core/Bootstrap.php
+++ b/typo3/sysext/core/Classes/Core/Bootstrap.php
@@ -633,7 +633,7 @@ protected function initializeErrorHandling()
                     );
                 }
         }
-        @ini_set('display_errors', $displayErrors);
+        @ini_set('display_errors', (string)$displayErrors);
 
         if (!empty($errorHandlerClassName)) {
             // Register an error handler for the given errorHandlerError
@@ -659,7 +659,7 @@ protected function initializeErrorHandling()
     protected function setMemoryLimit()
     {
         if ((int)$GLOBALS['TYPO3_CONF_VARS']['SYS']['setMemoryLimit'] > 16) {
-            @ini_set('memory_limit', ((int)$GLOBALS['TYPO3_CONF_VARS']['SYS']['setMemoryLimit'] . 'm'));
+            @ini_set('memory_limit', (string)((int)$GLOBALS['TYPO3_CONF_VARS']['SYS']['setMemoryLimit'] . 'm'));
         }
         return $this;
     }
@@ -972,7 +972,7 @@ public function initializeOutputCompression()
     {
         if (extension_loaded('zlib') && $GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel']) {
             if (MathUtility::canBeInterpretedAsInteger($GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel'])) {
-                @ini_set('zlib.output_compression_level', $GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel']);
+                @ini_set('zlib.output_compression_level', (string)$GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel']);
             }
             ob_start('ob_gzhandler');
         }
diff --git a/typo3/sysext/frontend/Classes/Http/RequestHandler.php b/typo3/sysext/frontend/Classes/Http/RequestHandler.php
index 7a5199ab8dab..3ffec3c76fc8 100644
--- a/typo3/sysext/frontend/Classes/Http/RequestHandler.php
+++ b/typo3/sysext/frontend/Classes/Http/RequestHandler.php
@@ -322,7 +322,7 @@ protected function initializeOutputCompression()
     {
         if ($GLOBALS['TYPO3_CONF_VARS']['FE']['compressionLevel'] && extension_loaded('zlib')) {
             if (MathUtility::canBeInterpretedAsInteger($GLOBALS['TYPO3_CONF_VARS']['FE']['compressionLevel'])) {
-                @ini_set('zlib.output_compression_level', $GLOBALS['TYPO3_CONF_VARS']['FE']['compressionLevel']);
+                @ini_set('zlib.output_compression_level', (string)$GLOBALS['TYPO3_CONF_VARS']['FE']['compressionLevel']);
             }
             ob_start([GeneralUtility::makeInstance(CompressionUtility::class), 'compressionOutputHandler']);
         }
diff --git a/typo3/sysext/install/Classes/Service/SessionService.php b/typo3/sysext/install/Classes/Service/SessionService.php
index 9629e3d3d70b..b2eda3694dca 100644
--- a/typo3/sysext/install/Classes/Service/SessionService.php
+++ b/typo3/sysext/install/Classes/Service/SessionService.php
@@ -74,11 +74,11 @@ public function __construct()
         session_set_save_handler([$this, 'open'], [$this, 'close'], [$this, 'read'], [$this, 'write'], [$this, 'destroy'], [$this, 'gc']);
         session_save_path($sessionSavePath);
         session_name($this->cookieName);
-        ini_set('session.cookie_path', GeneralUtility::getIndpEnv('TYPO3_SITE_PATH'));
+        ini_set('session.cookie_path', (string)GeneralUtility::getIndpEnv('TYPO3_SITE_PATH'));
         // Always call the garbage collector to clean up stale session files
-        ini_set('session.gc_probability', 100);
-        ini_set('session.gc_divisor', 100);
-        ini_set('session.gc_maxlifetime', $this->expireTimeInMinutes * 2 * 60);
+        ini_set('session.gc_probability', (string)100);
+        ini_set('session.gc_divisor', (string)100);
+        ini_set('session.gc_maxlifetime', (string)$this->expireTimeInMinutes * 2 * 60);
         if (\TYPO3\CMS\Core\Utility\PhpOptionsUtility::isSessionAutoStartEnabled()) {
             $sessionCreationError = 'Error: session.auto-start is enabled.<br />';
             $sessionCreationError .= 'The PHP option session.auto-start is enabled. Disable this option in php.ini or .htaccess:<br />';