diff --git a/rialto/Android.bp b/rialto/Android.bp
index ed9a284..7ac7136 100644
--- a/rialto/Android.bp
+++ b/rialto/Android.bp
@@ -76,6 +76,7 @@
 }
 
 prebuilt_etc {
+    // rialto_bin is a prebuilt target wrapping the signed bare-metal service VM.
     name: "rialto_bin",
     filename: "rialto.bin",
     target: {