diff --git a/src/Api/Controllers/V1/ElixFormsController.php b/src/Api/Controllers/V1/ElixFormsController.php
index f296a77..c49e642 100644
--- a/src/Api/Controllers/V1/ElixFormsController.php
+++ b/src/Api/Controllers/V1/ElixFormsController.php
@@ -41,7 +41,7 @@ class ElixFormsController
         $username = $this->config->secret('elixforms_api_username');
         $password = $this->config->secret('elixforms_api_password');
 
-        if (!is_string($username) || trim($username) === '' || !is_string($password) || $password === '') {
+        if (!\is_string($username) || trim($username) === '' || !\is_string($password) || $password === '') {
             throw new ElixFormsException('Credenziali elixForms non configurate.');
         }
 
@@ -85,7 +85,7 @@ class ElixFormsController
 
     private function requiredString(array $values, string $key): ?string
     {
-        if (!isset($values[$key]) || !is_string($values[$key])) {
+        if (!isset($values[$key]) || !\is_string($values[$key])) {
             return null;
         }
 
@@ -96,11 +96,11 @@ class ElixFormsController
 
     private function optionalNonEmptyString(array $values, string $key, string $default): ?string
     {
-        if (!array_key_exists($key, $values)) {
+        if (!\array_key_exists($key, $values)) {
             return $default;
         }
 
-        if (!is_string($values[$key])) {
+        if (!\is_string($values[$key])) {
             return null;
         }
 
@@ -112,7 +112,7 @@ class ElixFormsController
     private function requestId(array $instance)
     {
         foreach (['idDomanda', 'requestId', 'idRequest'] as $key) {
-            if (isset($instance[$key]) && (is_int($instance[$key]) || is_string($instance[$key]))) {
+            if (isset($instance[$key]) && (\is_int($instance[$key]) || \is_string($instance[$key]))) {
                 return $instance[$key];
             }
         }
diff --git a/src/Api/Core/Container.php b/src/Api/Core/Container.php
index dcd30bd..94fff17 100644
--- a/src/Api/Core/Container.php
+++ b/src/Api/Core/Container.php
@@ -53,7 +53,7 @@ class Container {
      */
     public function make(string $abstract) {
         // return existing singleton instance if already created
-        if (array_key_exists($abstract, $this->instances) && $this->instances[$abstract] !== null) {
+        if (\array_key_exists($abstract, $this->instances) && $this->instances[$abstract] !== null) {
             return $this->instances[$abstract];
         }
 
@@ -70,7 +70,7 @@ class Container {
             if (is_callable($concrete)) {
                 // factory receives the container
                 $object = $concrete($this);
-            } elseif (is_string($concrete) && class_exists($concrete)) {
+            } elseif (\is_string($concrete) && class_exists($concrete)) {
                 $object = $this->build($concrete);
             } else {
                 throw new \Exception("Invalid binding for [{$abstract}]");
@@ -78,7 +78,7 @@ class Container {
         }
 
         // if abstract was registered as singleton, cache the instance
-        if (array_key_exists($abstract, $this->instances)) {
+        if (\array_key_exists($abstract, $this->instances)) {
             $this->instances[$abstract] = $object;
         }