diff --git a/baseline.xml b/baseline.xml
new file mode 100644
index 00000000..9e572e4c
--- /dev/null
+++ b/baseline.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<files psalm-version="3.12.2@7c7ebd068f8acaba211d4a2c707c4ba90874fa26">
+  <file src="src/ComposerRequireChecker/NodeVisitor/DefinedSymbolCollector.php">
+    <NoInterfaceProperties occurrences="1">
+      <code>$node-&gt;namespacedName</code>
+    </NoInterfaceProperties>
+  </file>
+</files>
diff --git a/composer.json b/composer.json
index 1e0849fd..889acd0e 100644
--- a/composer.json
+++ b/composer.json
@@ -38,7 +38,8 @@
         "ext-zend-opcache": "*",
         "mikey179/vfsstream": "^1.6",
         "phpstan/phpstan": "^0.12",
-        "phpunit/phpunit": "^8.5.8"
+        "phpunit/phpunit": "^8.5.8",
+        "vimeo/psalm": "^3.12.2"
     },
     "config": {
         "optimize-autoloader": true,
diff --git a/psalm.xml b/psalm.xml
new file mode 100644
index 00000000..d5025223
--- /dev/null
+++ b/psalm.xml
@@ -0,0 +1,16 @@
+<?xml version="1.0"?>
+<psalm
+    errorLevel="4"
+    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/ComposerRequireChecker/ASTLocator/LocateASTFromFiles.php b/src/ComposerRequireChecker/ASTLocator/LocateASTFromFiles.php
index 7eebc726..5a509811 100644
--- a/src/ComposerRequireChecker/ASTLocator/LocateASTFromFiles.php
+++ b/src/ComposerRequireChecker/ASTLocator/LocateASTFromFiles.php
@@ -25,9 +25,7 @@ public function __construct(Parser $parser, ?ErrorHandler $errorHandler)
     }
 
     /**
-     * @param Traversable|string[] $files
-     *
-     * @return Traversable|array[] a series of AST roots, one for each given file
+     * @return Traversable a series of AST roots, one for each given file
      */
     public function __invoke(Traversable $files): Traversable
     {
diff --git a/src/ComposerRequireChecker/DefinedSymbolsLocator/LocateDefinedSymbolsFromASTRoots.php b/src/ComposerRequireChecker/DefinedSymbolsLocator/LocateDefinedSymbolsFromASTRoots.php
index 1e5fef11..81378aad 100644
--- a/src/ComposerRequireChecker/DefinedSymbolsLocator/LocateDefinedSymbolsFromASTRoots.php
+++ b/src/ComposerRequireChecker/DefinedSymbolsLocator/LocateDefinedSymbolsFromASTRoots.php
@@ -10,7 +10,7 @@
 final class LocateDefinedSymbolsFromASTRoots
 {
     /**
-     * @param Traversable|array[] $ASTs a series of AST roots
+     * @param Traversable $ASTs a series of AST roots
      *
      * @return string[] all the found symbols
      */
diff --git a/src/ComposerRequireChecker/FileLocator/LocateFilesByGlobPattern.php b/src/ComposerRequireChecker/FileLocator/LocateFilesByGlobPattern.php
index 84ad1052..190ef00a 100644
--- a/src/ComposerRequireChecker/FileLocator/LocateFilesByGlobPattern.php
+++ b/src/ComposerRequireChecker/FileLocator/LocateFilesByGlobPattern.php
@@ -2,7 +2,7 @@
 
 namespace ComposerRequireChecker\FileLocator;
 
-
+use Generator;
 use Webmozart\Glob\Glob;
 
 class LocateFilesByGlobPattern
@@ -11,10 +11,10 @@ class LocateFilesByGlobPattern
     /**
      * @param string[] $globPatterns a list of glob patterns to find files in
      * @param string $rootDir the root directory that should be used when patterns are relative paths
-     * @return iterable|string[] the files found by the given glob patterns
+     * @return Generator the files found by the given glob patterns
      * @see https://github.com/webmozart/glob
      */
-    public function __invoke(array $globPatterns = [], string $rootDir): iterable
+    public function __invoke(array $globPatterns = [], string $rootDir): Generator
     {
         foreach ($globPatterns as $globPattern) {
             yield from Glob::glob(rtrim($rootDir, '/') . '/' . $globPattern);
diff --git a/src/ComposerRequireChecker/NodeVisitor/UsedSymbolCollector.php b/src/ComposerRequireChecker/NodeVisitor/UsedSymbolCollector.php
index 34bacd4c..acbc9fa4 100644
--- a/src/ComposerRequireChecker/NodeVisitor/UsedSymbolCollector.php
+++ b/src/ComposerRequireChecker/NodeVisitor/UsedSymbolCollector.php
@@ -123,11 +123,16 @@ private function recordFunctionReturnTypeUsage(Node $node)
         if ($node instanceof Node\Stmt\Function_
             || $node instanceof Node\Stmt\ClassMethod
         ) {
-            if ($node->getReturnType() instanceof Node\Name) {
-                $this->recordUsageOf($node->getReturnType());
+            $returnType = $node->getReturnType();
+
+            if ($returnType instanceof Node\Name) {
+                $this->recordUsageOf($returnType);
+            }
+            if ($returnType instanceof Node\Identifier) {
+                $this->recordUsageOfByString($returnType->toString());
             }
-            if (is_string($node->getReturnType()) || $node->getReturnType() instanceof Node\Identifier) {
-                $this->recordUsageOfByString($node->getReturnType());
+            if (is_string($returnType)) {
+                $this->recordUsageOfByString($returnType);
             }
         }
     }
diff --git a/src/ComposerRequireChecker/UsedSymbolsLocator/LocateUsedSymbolsFromASTRoots.php b/src/ComposerRequireChecker/UsedSymbolsLocator/LocateUsedSymbolsFromASTRoots.php
index 01b817cb..2d05dc8d 100644
--- a/src/ComposerRequireChecker/UsedSymbolsLocator/LocateUsedSymbolsFromASTRoots.php
+++ b/src/ComposerRequireChecker/UsedSymbolsLocator/LocateUsedSymbolsFromASTRoots.php
@@ -10,7 +10,7 @@
 final class LocateUsedSymbolsFromASTRoots
 {
     /**
-     * @param Traversable|array[] $ASTs a series of AST roots
+     * @param Traversable $ASTs a series of AST roots
      *
      * @return string[] all the found symbols
      */