diff --git a/tools/aapt2/Resources.proto b/tools/aapt2/Resources.proto
index 73b568e77689c..9a1d94288363c 100644
--- a/tools/aapt2/Resources.proto
+++ b/tools/aapt2/Resources.proto
@@ -151,10 +151,12 @@ message Overlayable {
 // Represents an overlayable <item> declaration within an <overlayable> tag.
 message OverlayableItem {
   enum Policy {
-    PUBLIC = 0;
-    SYSTEM = 1;
-    VENDOR = 2;
-    PRODUCT = 3;
+    NONE = 0;
+    PUBLIC = 1;
+    SYSTEM = 2;
+    VENDOR = 3;
+    PRODUCT = 4;
+    SIGNATURE = 5;
   }
 
   // The location of the <item> declaration in source.