diff --git a/src/Symfony/Component/Finder/Finder.php b/src/Symfony/Component/Finder/Finder.php
index 011f661aab..4cf723bf33 100644
--- a/src/Symfony/Component/Finder/Finder.php
+++ b/src/Symfony/Component/Finder/Finder.php
@@ -624,7 +624,13 @@ class Finder implements \IteratorAggregate, \Countable
         }
 
         if (1 === \count($this->dirs) && 0 === \count($this->iterators)) {
-            return $this->searchInDirectory($this->dirs[0]);
+            $iterator = $this->searchInDirectory($this->dirs[0]);
+
+            if ($this->sort || $this->reverseSorting) {
+                $iterator = (new Iterator\SortableIterator($iterator, $this->sort, $this->reverseSorting))->getIterator();
+            }
+
+            return $iterator;
         }
 
         $iterator = new \AppendIterator();
@@ -636,6 +642,10 @@ class Finder implements \IteratorAggregate, \Countable
             $iterator->append($it);
         }
 
+        if ($this->sort || $this->reverseSorting) {
+            $iterator = (new Iterator\SortableIterator($iterator, $this->sort, $this->reverseSorting))->getIterator();
+        }
+
         return $iterator;
     }
 
@@ -782,11 +792,6 @@ class Finder implements \IteratorAggregate, \Countable
             $iterator = new Iterator\PathFilterIterator($iterator, $this->paths, $notPaths);
         }
 
-        if ($this->sort || $this->reverseSorting) {
-            $iteratorAggregate = new Iterator\SortableIterator($iterator, $this->sort, $this->reverseSorting);
-            $iterator = $iteratorAggregate->getIterator();
-        }
-
         return $iterator;
     }
 
diff --git a/src/Symfony/Component/Finder/Tests/FinderTest.php b/src/Symfony/Component/Finder/Tests/FinderTest.php
index 9a12e85e25..efdb4c7447 100644
--- a/src/Symfony/Component/Finder/Tests/FinderTest.php
+++ b/src/Symfony/Component/Finder/Tests/FinderTest.php
@@ -832,6 +832,39 @@ class FinderTest extends Iterator\RealIteratorTestCase
         ]), $finder->in(self::$tmpDir)->getIterator());
     }
 
+    public function testSortAcrossDirectories()
+    {
+        $finder = $this->buildFinder()
+            ->in([
+                self::$tmpDir,
+                self::$tmpDir.'/qux',
+                self::$tmpDir.'/foo',
+            ])
+            ->depth(0)
+            ->files()
+            ->filter(static function (\SplFileInfo $file): bool {
+                return '' !== $file->getExtension();
+            })
+            ->sort(static function (\SplFileInfo $a, \SplFileInfo $b): int {
+                return strcmp($a->getExtension(), $b->getExtension()) ?: strcmp($a->getFilename(), $b->getFilename());
+            })
+        ;
+
+        $this->assertOrderedIterator($this->toAbsolute([
+            'qux_0_1.php',
+            'qux_1000_1.php',
+            'qux_1002_0.php',
+            'qux_10_2.php',
+            'qux_12_0.php',
+            'qux_2_0.php',
+            'test.php',
+            'qux/baz_100_1.py',
+            'qux/baz_1_2.py',
+            'test.py',
+            'foo/bar.tmp',
+        ]), $finder->getIterator());
+    }
+
     public function testFilter()
     {
         $finder = $this->buildFinder();
diff --git a/src/Symfony/Component/Finder/Tests/Iterator/IteratorTestCase.php b/src/Symfony/Component/Finder/Tests/Iterator/IteratorTestCase.php
index c7dfd79e30..9bfc479de5 100644
--- a/src/Symfony/Component/Finder/Tests/Iterator/IteratorTestCase.php
+++ b/src/Symfony/Component/Finder/Tests/Iterator/IteratorTestCase.php
@@ -31,7 +31,8 @@ abstract class IteratorTestCase extends TestCase
 
     protected function assertOrderedIterator($expected, \Traversable $iterator)
     {
-        $values = array_map(function (\SplFileInfo $fileinfo) { return $fileinfo->getPathname(); }, iterator_to_array($iterator));
+        $values = array_map(function (\SplFileInfo $fileinfo) { return str_replace('/', \DIRECTORY_SEPARATOR, $fileinfo->getPathname()); }, iterator_to_array($iterator));
+        $expected = array_map(function ($path) { return str_replace('/', \DIRECTORY_SEPARATOR, $path); }, $expected);
 
         $this->assertEquals($expected, array_values($values));
     }