diff --git a/src/ClassMap.php b/src/ClassMap.php
index 797efc6..72304da 100644
--- a/src/ClassMap.php
+++ b/src/ClassMap.php
@@ -94,7 +94,7 @@ public function getAmbiguousClasses($duplicatesFilter = '{/(test|fixture|example
 
         $ambiguousClasses = [];
         foreach ($this->ambiguousClasses as $class => $paths) {
-            $paths = array_filter($paths, function ($path) use ($duplicatesFilter) {
+            $paths = array_filter($paths, function ($path) use ($duplicatesFilter): bool {
                 return !Preg::isMatch($duplicatesFilter, strtr($path, '\\', '/'));
             });
             if (\count($paths) > 0) {
diff --git a/src/ClassMapGenerator.php b/src/ClassMapGenerator.php
index 2bfa1ed..55ef593 100644
--- a/src/ClassMapGenerator.php
+++ b/src/ClassMapGenerator.php
@@ -280,7 +280,7 @@ private function filterByNamespace(array $classes, string $filePath, string $bas
      * @param  string $path
      * @return bool
      */
-    private static function isAbsolutePath(string $path)
+    private static function isAbsolutePath(string $path): bool
     {
         return strpos($path, '/') === 0 || substr($path, 1, 1) === ':' || strpos($path, '\\\\') === 0;
     }
@@ -294,7 +294,7 @@ private static function isAbsolutePath(string $path)
      * @param  string $path Path to the file or directory
      * @return string
      */
-    private static function normalizePath(string $path)
+    private static function normalizePath(string $path): string
     {
         $parts = [];
         $path = strtr($path, '\\', '/');