diff --git a/composer.json b/composer.json
index 4a996d4..311c3e2 100644
--- a/composer.json
+++ b/composer.json
@@ -15,8 +15,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^8|^6",
-        "amphp/php-cs-fixer-config": "dev-master",
-        "vimeo/psalm": "dev-master"
+        "amphp/php-cs-fixer-config": "dev-master"
     },
     "autoload": {
         "psr-4": {
diff --git a/psalm.xml b/psalm.xml
new file mode 100644
index 0000000..8dc065a
--- /dev/null
+++ b/psalm.xml
@@ -0,0 +1,15 @@
+<?xml version="1.0"?>
+<psalm
+    errorLevel="5"
+    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" />
+        </ignoreFiles>
+    </projectFiles>
+</psalm>