diff --git a/.travis.yml b/.travis.yml
index a9f9cd8..c6ac198 100755
--- a/.travis.yml
+++ b/.travis.yml
@@ -18,6 +18,7 @@ before_script:
 
 script:
   - vendor/bin/phpunit
+  - vendor/bin/psalm --shepherd
 
 # Use Travis' new container-based infrastructure.
 # See http://docs.travis-ci.com/user/migrating-from-legacy/#How-can-I-use-container-based-infrastructure%3F
diff --git a/README.md b/README.md
index 7bdd4f8..6065f49 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,7 @@
 [![Build Status](https://travis-ci.org/myclabs/php-enum.png?branch=master)](https://travis-ci.org/myclabs/php-enum)
 [![Latest Stable Version](https://poser.pugx.org/myclabs/php-enum/version.png)](https://packagist.org/packages/myclabs/php-enum)
 [![Total Downloads](https://poser.pugx.org/myclabs/php-enum/downloads.png)](https://packagist.org/packages/myclabs/php-enum)
+[![psalm](https://shepherd.dev/github/myclabs/php-enum/coverage.svg)](https://shepherd.dev/github/myclabs/php-enum)
 
 Maintenance for this project is [supported via Tidelift](https://tidelift.com/subscription/pkg/packagist-myclabs-php-enum?utm_source=packagist-myclabs-php-enum&utm_medium=referral&utm_campaign=readme).
 
diff --git a/composer.json b/composer.json
index 871156d..1c7ba1c 100644
--- a/composer.json
+++ b/composer.json
@@ -23,10 +23,11 @@
     },
     "require": {
         "php": ">=7.1",
-        "ext-json": "*"
+        "ext-json": "*",
+        "vimeo/psalm": "^3.8"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8.35|^5.7|^6.0",
+        "phpunit/phpunit": "^7",
         "squizlabs/php_codesniffer": "1.*"
     }
 }
diff --git a/psalm.xml b/psalm.xml
new file mode 100644
index 0000000..b07e929
--- /dev/null
+++ b/psalm.xml
@@ -0,0 +1,20 @@
+<?xml version="1.0"?>
+<psalm
+    totallyTyped="true"
+    resolveFromConfigFile="true"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns="https://getpsalm.org/schema/config"
+    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
+>
+    <projectFiles>
+        <directory name="src" />
+        <ignoreFiles>
+            <directory name="vendor" />
+            <directory name="src/PHPUnit" />
+        </ignoreFiles>
+    </projectFiles>
+
+    <issueHandlers>
+        <MixedAssignment errorLevel="info" />
+    </issueHandlers>
+</psalm>
diff --git a/src/Enum.php b/src/Enum.php
index 3bce0dc..5c15251 100644
--- a/src/Enum.php
+++ b/src/Enum.php
@@ -14,6 +14,9 @@
  * @author Matthieu Napoli <matthieu@mnapoli.fr>
  * @author Daniel Costa <danielcosta@gmail.com>
  * @author Mirosław Filip <mirfilip@gmail.com>
+ *
+ * @template T
+ * @psalm-immutable
  */
 abstract class Enum implements \JsonSerializable
 {
@@ -21,6 +24,7 @@ abstract class Enum implements \JsonSerializable
      * Enum value
      *
      * @var mixed
+     * @psalm-var T
      */
     protected $value;
 
@@ -28,6 +32,7 @@ abstract class Enum implements \JsonSerializable
      * Store existing constants in a static cache per object.
      *
      * @var array
+     * @psalm-var array<class-string, array<string, mixed>>
      */
     protected static $cache = [];
 
@@ -36,6 +41,8 @@ abstract class Enum implements \JsonSerializable
      *
      * @param mixed $value
      *
+     * @psalm-param T $value
+     * @psalm-suppress InvalidCast
      * @throws \UnexpectedValueException if incompatible type is given.
      */
     public function __construct($value)
@@ -45,7 +52,7 @@ public function __construct($value)
         }
 
         if (!$this->isValid($value)) {
-            throw new \UnexpectedValueException("Value '$value' is not part of the enum " . \get_called_class());
+            throw new \UnexpectedValueException("Value '$value' is not part of the enum " . static::class);
         }
 
         $this->value = $value;
@@ -53,6 +60,7 @@ public function __construct($value)
 
     /**
      * @return mixed
+     * @psalm-return T
      */
     public function getValue()
     {
@@ -62,6 +70,7 @@ public function getValue()
     /**
      * Returns the enum key (i.e. the constant name).
      *
+     * @psalm-pure
      * @return mixed
      */
     public function getKey()
@@ -70,6 +79,7 @@ public function getKey()
     }
 
     /**
+     * @psalm-suppress InvalidCast
      * @return string
      */
     public function __toString()
@@ -83,13 +93,14 @@ public function __toString()
      *
      * This method is final, for more information read https://github.com/myclabs/php-enum/issues/4
      *
+     * @psalm-param mixed $variable
      * @return bool
      */
     final public function equals($variable = null): bool
     {
         return $variable instanceof self
             && $this->getValue() === $variable->getValue()
-            && \get_called_class() === \get_class($variable);
+            && static::class === \get_class($variable);
     }
 
     /**
@@ -121,11 +132,14 @@ public static function values()
     /**
      * Returns all possible values as an array
      *
+     * @psalm-pure
+     * @psalm-return array<string, mixed>
      * @return array Constant name in key, constant value in value
      */
     public static function toArray()
     {
-        $class = \get_called_class();
+        $class = static::class;
+
         if (!isset(static::$cache[$class])) {
             $reflection            = new \ReflectionClass($class);
             static::$cache[$class] = $reflection->getConstants();
@@ -138,6 +152,7 @@ public static function toArray()
      * Check if is valid enum value
      *
      * @param $value
+     * @psalm-param mixed $value
      *
      * @return bool
      */
@@ -150,6 +165,7 @@ public static function isValid($value)
      * Check if is valid enum key
      *
      * @param $key
+     * @psalm-param string $key
      *
      * @return bool
      */
@@ -165,6 +181,8 @@ public static function isValidKey($key)
      *
      * @param $value
      *
+     * @psalm-param mixed $value
+     * @psalm-pure
      * @return mixed
      */
     public static function search($value)
@@ -188,7 +206,7 @@ public static function __callStatic($name, $arguments)
             return new static($array[$name]);
         }
 
-        throw new \BadMethodCallException("No static method or enum constant '$name' in class " . \get_called_class());
+        throw new \BadMethodCallException("No static method or enum constant '$name' in class " . static::class);
     }
 
     /**