diff --git a/src/Core/Config/Cache/PConfigCache.php b/src/Core/Config/Cache/PConfigCache.php
index b03d86f41e..d6b1c9b316 100644
--- a/src/Core/Config/Cache/PConfigCache.php
+++ b/src/Core/Config/Cache/PConfigCache.php
@@ -34,7 +34,7 @@ class PConfigCache
 	 * @param int   $uid
 	 * @param array $config
 	 */
-	public function load(int $uid, array $config)
+	public function load($uid, array $config)
 	{
 		$categories = array_keys($config);
 
@@ -62,7 +62,7 @@ class PConfigCache
 	 *
 	 * @return null|string The value of the config entry or null if not set
 	 */
-	public function get(int $uid, string $cat, string $key = null)
+	public function get($uid, string $cat, string $key = null)
 	{
 		if (isset($this->config[$uid][$cat][$key])) {
 			return $this->config[$uid][$cat][$key];
@@ -85,7 +85,7 @@ class PConfigCache
 	 *
 	 * @return bool Set successful
 	 */
-	public function set(int $uid, string $cat, string $key, $value)
+	public function set($uid, string $cat, string $key, $value)
 	{
 		if (!isset($this->config[$uid]) || !is_array($this->config[$uid])) {
 			$this->config[$uid] = [];
@@ -116,7 +116,7 @@ class PConfigCache
 	 *
 	 * @return bool true, if deleted
 	 */
-	public function delete(int $uid, string $cat, string $key)
+	public function delete($uid, string $cat, string $key)
 	{
 		if (isset($this->config[$uid][$cat][$key])) {
 			unset($this->config[$uid][$cat][$key]);
diff --git a/src/Core/Config/JitPConfiguration.php b/src/Core/Config/JitPConfiguration.php
index 8ad65eff1a..82fcbe110c 100644
--- a/src/Core/Config/JitPConfiguration.php
+++ b/src/Core/Config/JitPConfiguration.php
@@ -32,10 +32,10 @@ class JitPConfiguration extends PConfiguration
 	 * {@inheritDoc}
 	 *
 	 */
-	public function load(int $uid, string $cat = 'config')
+	public function load($uid, string $cat = 'config')
 	{
-		// If not connected, do nothing
-		if (!$this->configModel->isConnected()) {
+		// If not connected or no uid, do nothing
+		if (!is_int($uid) || !$this->configModel->isConnected()) {
 			return;
 		}
 
@@ -54,8 +54,12 @@ class JitPConfiguration extends PConfiguration
 	/**
 	 * {@inheritDoc}
 	 */
-	public function get(int $uid, string $cat, string $key, $default_value = null, bool $refresh = false)
+	public function get($uid, string $cat, string $key, $default_value = null, bool $refresh = false)
 	{
+		if (!is_int($uid)) {
+			return $default_value;
+		}
+
 		// if the value isn't loaded or refresh is needed, load it to the cache
 		if ($this->configModel->isConnected() &&
 		    (empty($this->db_loaded[$uid][$cat][$key]) ||
@@ -80,8 +84,12 @@ class JitPConfiguration extends PConfiguration
 	/**
 	 * {@inheritDoc}
 	 */
-	public function set(int $uid, string $cat, string $key, $value)
+	public function set($uid, string $cat, string $key, $value)
 	{
+		if (!is_int($uid)) {
+			return false;
+		}
+
 		// set the cache first
 		$cached = $this->configCache->set($uid, $cat, $key, $value);
 
@@ -100,8 +108,12 @@ class JitPConfiguration extends PConfiguration
 	/**
 	 * {@inheritDoc}
 	 */
-	public function delete(int $uid, string $cat, string $key)
+	public function delete($uid, string $cat, string $key)
 	{
+		if (!is_int($uid)) {
+			return false;
+		}
+
 		$cacheRemoved = $this->configCache->delete($uid, $cat, $key);
 
 		if (isset($this->db_loaded[$uid][$cat][$key])) {
diff --git a/src/Core/Config/PConfiguration.php b/src/Core/Config/PConfiguration.php
index fd4ef2bd3f..a00da819a4 100644
--- a/src/Core/Config/PConfiguration.php
+++ b/src/Core/Config/PConfiguration.php
@@ -55,7 +55,7 @@ abstract class PConfiguration
 	 * @see PConfigCache )
 	 *
 	 */
-	abstract public function load(int $uid, string $cat = 'config');
+	abstract public function load($uid, string $cat = 'config');
 
 	/**
 	 * Get a particular user's config variable given the category name
@@ -73,7 +73,7 @@ abstract class PConfiguration
 	 *
 	 * @return mixed Stored value or null if it does not exist
 	 */
-	abstract public function get(int $uid, string $cat, string $key, $default_value = null, bool $refresh = false);
+	abstract public function get($uid, string $cat, string $key, $default_value = null, bool $refresh = false);
 
 	/**
 	 * Sets a configuration value for a user
@@ -90,7 +90,7 @@ abstract class PConfiguration
 	 *
 	 * @return bool Operation success
 	 */
-	abstract public function set(int $uid, string $cat, string $key, $value);
+	abstract public function set($uid, string $cat, string $key, $value);
 
 	/**
 	 * Deletes the given key from the users's configuration.
@@ -105,5 +105,5 @@ abstract class PConfiguration
 	 *
 	 * @return bool
 	 */
-	abstract public function delete(int $uid, string $cat, string $key);
+	abstract public function delete($uid, string $cat, string $key);
 }
diff --git a/src/Core/Config/PreloadPConfiguration.php b/src/Core/Config/PreloadPConfiguration.php
index 1c2dfba4f7..dd1a72bafd 100644
--- a/src/Core/Config/PreloadPConfiguration.php
+++ b/src/Core/Config/PreloadPConfiguration.php
@@ -31,10 +31,10 @@ class PreloadPConfiguration extends PConfiguration
 	 * This loads all config values everytime load is called
 	 *
 	 */
-	public function load(int $uid, string $cat = 'config')
+	public function load($uid, string $cat = 'config')
 	{
-		// Don't load the whole configuration twice
-		if (!empty($this->config_loaded[$uid])) {
+		// Don't load the whole configuration twice or with invalid uid
+		if (!is_int($uid) || !empty($this->config_loaded[$uid])) {
 			return;
 		}
 
@@ -53,8 +53,12 @@ class PreloadPConfiguration extends PConfiguration
 	/**
 	 * {@inheritDoc}
 	 */
-	public function get(int $uid, string $cat, string $key, $default_value = null, bool $refresh = false)
+	public function get($uid, string $cat, string $key, $default_value = null, bool $refresh = false)
 	{
+		if (!is_int($uid)) {
+			return $default_value;
+		}
+
 		if (empty($this->config_loaded[$uid])) {
 			$this->load($uid);
 		} elseif ($refresh) {
@@ -75,8 +79,12 @@ class PreloadPConfiguration extends PConfiguration
 	/**
 	 * {@inheritDoc}
 	 */
-	public function set(int $uid, string $cat, string $key, $value)
+	public function set($uid, string $cat, string $key, $value)
 	{
+		if (!is_int($uid)) {
+			return false;
+		}
+
 		if (empty($this->config_loaded[$uid])) {
 			$this->load($uid);
 		}
@@ -97,8 +105,12 @@ class PreloadPConfiguration extends PConfiguration
 	/**
 	 * {@inheritDoc}
 	 */
-	public function delete(int $uid, string $cat, string $key)
+	public function delete($uid, string $cat, string $key)
 	{
+		if (!is_int($uid)) {
+			return false;
+		}
+
 		if (empty($this->config_loaded[$uid])) {
 			$this->load($uid);
 		}
diff --git a/tests/src/Core/Config/PConfigurationTest.php b/tests/src/Core/Config/PConfigurationTest.php
index adc9f267a1..1d5e9c0a17 100644
--- a/tests/src/Core/Config/PConfigurationTest.php
+++ b/tests/src/Core/Config/PConfigurationTest.php
@@ -452,4 +452,22 @@ abstract class PConfigurationTest extends MockedTest
 		$this->assertConfig($data2['uid'], 'cat1', $data2['data']['cat1']);
 		$this->assertConfig($data2['uid'], 'cat2', $data2['data']['cat2']);
 	}
+
+	/**
+	 * Test when using an invalid UID
+	 * @todo check it the clean way before using the config class
+	 */
+	public function testInvalidUid()
+	{
+		// bad UID!
+		$uid = null;
+
+		$this->testedConfig = $this->getInstance();
+
+		$this->assertNull($this->testedConfig->get($uid, 'cat1', 'cat2'));
+		$this->assertEquals('fallback!', $this->testedConfig->get($uid, 'cat1', 'cat2', 'fallback!'));
+
+		$this->assertFalse($this->testedConfig->set($uid, 'cat1', 'key1', 'doesn\'t matter!'));
+		$this->assertFalse($this->testedConfig->delete($uid, 'cat1', 'key1'));
+	}
 }