diff --git a/.github/workflows/continuous-integration.yml b/.github/workflows/continuous-integration.yml
index f5fc336eb..81901f401 100644
--- a/.github/workflows/continuous-integration.yml
+++ b/.github/workflows/continuous-integration.yml
@@ -44,8 +44,8 @@ jobs:
       - name: "Check cs"
         run: make php-cs-check
 
-  static-code-analysis:
-    name: "Static Code Analysis"
+  static-code-analysis-phpstan:
+    name: "Static Code Analysis by PHPStan"
 
     runs-on: ubuntu-latest
 
@@ -88,6 +88,50 @@ jobs:
       - name: PHPStan
         run: make phpstan
 
+  static-code-analysis-psalm:
+    name: "Static Code Analysis by Psalm"
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: "Checkout"
+        uses: actions/checkout@v2
+
+      - name: "Cache tools installed with phive"
+        uses: actions/cache@v2
+        with:
+          path: |
+            ~~/.phive
+            ./tools
+          key: ${{ runner.os }}-phive-cache-${{ hashFiles('**/.phive/phars.xml') }}
+          restore-keys: |
+            phive-cache-
+
+      - name: "Cache dependencies installed with composer"
+        uses: actions/cache@v2
+        with:
+          path: ~/.composer/cache
+          key: composer-cache-${{ hashFiles('**/composer.lock') }}
+          restore-keys: |
+            composer-cache-
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '7.2'
+          extensions: mbstring, xml, ctype, iconv
+          coverage: none
+          tools: phive
+
+      - name: "Install tools with phive"
+        run: make tools-install
+
+      - name: "Install dependencies with composer"
+        run: composer install --no-interaction --no-progress --no-suggest --optimize-autoloader
+
+      - name: Psalm
+        run: make psalm
+
   tests:
     name: "PHP ${{ matrix.php-versions }} Test"
 
diff --git a/.phive/phars.xml b/.phive/phars.xml
index 1afae8985..ac1d1c830 100644
--- a/.phive/phars.xml
+++ b/.phive/phars.xml
@@ -3,5 +3,6 @@
   <phar name="php-cs-fixer" version="^2.16.3" installed="2.16.3" location="./tools/php-cs-fixer" copy="true"/>
   <phar name="phpunit" version="^8.5.6" installed="8.5.6" location="./tools/phpunit" copy="true"/>
   <phar name="phpstan" version="^0.12.29" installed="0.12.29" location="./tools/phpstan" copy="true"/>
+  <phar name="psalm" version="^3.12.2" installed="3.12.2" location="./tools/psalm" copy="true"/>
   <phar name="humbug/box" version="^3.8.4" installed="3.8.4" location="./tools/box" copy="true"/>
 </phive>
diff --git a/Makefile b/Makefile
index e402c30c4..d51c0f18f 100644
--- a/Makefile
+++ b/Makefile
@@ -4,6 +4,7 @@ PHP_BIN := php
 PHIVE_BIN := phive
 PHP_CS_FIXER_BIN := ./tools/php-cs-fixer
 PHPSTAN_BIN	:= ./tools/phpstan
+PSALM_BIN	:= ./tools/psalm
 PHPUNIT_BIN	:= ./tools/phpunit
 
 .PHONY: build tools-install composer-install tests tests-coverage gpg php-cs-check php-cs-fix phpstan
@@ -34,6 +35,9 @@ php-cs-fix:																		## run cs fixer
 phpstan:
 	$(PHPSTAN_BIN) analyse
 
+psalm:
+	$(PSALM_BIN) analyse
+
 gpg:
 	gpg --detach-sign --armor --output deptrac.phar.asc deptrac.phar
 	gpg --verify deptrac.phar.asc deptrac.phar
diff --git a/baseline.xml b/baseline.xml
new file mode 100644
index 000000000..e8894fde0
--- /dev/null
+++ b/baseline.xml
@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<files psalm-version="3.12.2@7c7ebd068f8acaba211d4a2c707c4ba90874fa26">
+  <file src="src/OutputFormatter/GraphVizOutputFormatter.php">
+    <InvalidScalarArgument occurrences="2">
+      <code>$layer</code>
+      <code>$layerDependOn</code>
+    </InvalidScalarArgument>
+  </file>
+</files>
diff --git a/psalm.xml b/psalm.xml
new file mode 100644
index 000000000..8f098e3ec
--- /dev/null
+++ b/psalm.xml
@@ -0,0 +1,16 @@
+<?xml version="1.0"?>
+<psalm
+    errorLevel="3"
+    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"
+    errorBaseline="./baseline.xml"
+>
+    <projectFiles>
+        <directory name="src" />
+        <ignoreFiles>
+            <directory name="vendor" />
+        </ignoreFiles>
+    </projectFiles>
+</psalm>
diff --git a/src/AstRunner/AstParser/NikicPhpParser/NikicPhpParser.php b/src/AstRunner/AstParser/NikicPhpParser/NikicPhpParser.php
index 736374f52..d2238cac8 100644
--- a/src/AstRunner/AstParser/NikicPhpParser/NikicPhpParser.php
+++ b/src/AstRunner/AstParser/NikicPhpParser/NikicPhpParser.php
@@ -91,7 +91,9 @@ public function getAstForClassReference(AstClassReference $classReference): ?Nod
             return self::$classAstMap[$classLikeName];
         }
 
-        if (null === $classReference->getFileReference()) {
+        $astFileReference = $classReference->getFileReference();
+
+        if (null === $astFileReference) {
             return null;
         }
 
@@ -102,9 +104,7 @@ static function (Node $node): bool {
         );
 
         $this->traverser->addVisitor($findingVisitor);
-        $this->traverser->traverse(
-            $this->fileParser->parse(new \SplFileInfo($classReference->getFileReference()->getFilepath()))
-        );
+        $this->traverser->traverse($this->fileParser->parse(new \SplFileInfo($astFileReference->getFilepath())));
         $this->traverser->removeVisitor($findingVisitor);
 
         /** @var Node\Stmt\ClassLike[] $classLikeNodes */
diff --git a/src/FileResolver.php b/src/FileResolver.php
index 58df2b546..60387d89d 100644
--- a/src/FileResolver.php
+++ b/src/FileResolver.php
@@ -4,6 +4,7 @@
 
 namespace SensioLabs\Deptrac;
 
+use Iterator;
 use SensioLabs\Deptrac\Configuration\Configuration;
 use SplFileInfo;
 use Symfony\Component\Finder\Finder;
@@ -24,11 +25,13 @@ public function resolve(Configuration $configuration): array
             ->ignoreVCS(true)
             ->notPath($configuration->getExcludeFiles());
 
-        $finder = new PathNameFilterIterator(
-            $finder->getIterator(),
-            [],
-            $configuration->getExcludeFiles()
-        );
+        $customFilterIterator = $finder->getIterator();
+
+        if (!$customFilterIterator instanceof Iterator) {
+            throw new \RuntimeException('unable to create an interator for the configured paths');
+        }
+
+        $finder = new PathNameFilterIterator($customFilterIterator, [], $configuration->getExcludeFiles());
 
         return iterator_to_array($finder);
     }