diff --git a/root.bp b/root.bp
index d32cf8ad3..8ba1c124f 100644
--- a/root.bp
+++ b/root.bp
@@ -2,20 +2,23 @@ subname = "Android.bp"
 
 subdirs = [
     "build/blueprint",
-    "build/kati",
     "build/soong",
+]
+
+optional_subdirs = [
     "bionic/*",
+    "build/kati",
+    "build/tools/*",
     "dalvik",
     "external/*",
     "frameworks/base",
     "frameworks/native/libs/*",
     "hardware/*",
     "libcore",
+    "packages/apps/HTMLViewer",
     "prebuilts/ndk",
     "prebuilts/sdk",
     "system/core/*",
-    "packages/apps/HTMLViewer",
-    "build/tools/*",
-    "system/security/*",
     "system/keymaster",
+    "system/security/*",
 ]