diff --git a/phpunit/src/FileScannerTest.php b/phpunit/src/FileScannerTest.php
index 8a3c1e26..544cc9af 100644
--- a/phpunit/src/FileScannerTest.php
+++ b/phpunit/src/FileScannerTest.php
@@ -141,6 +141,15 @@ class FileScannerTest extends TestCase
         $scanner = new FileScanner($tmpDir);
         $files = $scanner->scan();
 
+        $this->assertSame([
+            $tmpDir . '/helper.c',
+            $tmpDir . '/lib.m',
+            $tmpDir . '/main.php',
+            $tmpDir . '/math.S',
+            $tmpDir . '/module.cc',
+            $tmpDir . '/sub/nested.cpp',
+        ], $files);
+
         // Python and Markdown should not be included
         $this->assertContains($tmpDir . '/main.php', $files);
         $this->assertContains($tmpDir . '/helper.c', $files);
diff --git a/src/Build/FileScanner.php b/src/Build/FileScanner.php
index 6828b920..ee716ded 100644
--- a/src/Build/FileScanner.php
+++ b/src/Build/FileScanner.php
@@ -100,6 +100,12 @@ class FileScanner
             }
         }
 
+        // RecursiveDirectoryIterator follows filesystem directory-entry order,
+        // which differs between a fresh checkout and a long-lived worktree.
+        // Preparation allocates symbol-cache IDs while visiting this list, so
+        // keep both generated code and cache classification deterministic.
+        sort($files, SORT_STRING);
+
         return $files;
     }