diff --git a/java/java.go b/java/java.go
index 45eb693..2bbb5b1 100644
--- a/java/java.go
+++ b/java/java.go
@@ -57,6 +57,10 @@
 	ctx.RegisterModuleType("java_host_for_device", HostForDeviceFactory)
 	ctx.RegisterModuleType("dex_import", DexImportFactory)
 
+	// This mutator registers dependencies on dex2oat for modules that should be
+	// dexpreopted. This is done late when the final variants have been
+	// established, to not get the dependencies split into the wrong variants and
+	// to support the checks in dexpreoptDisabled().
 	ctx.FinalDepsMutators(func(ctx android.RegisterMutatorsContext) {
 		ctx.BottomUp("dexpreopt_tool_deps", dexpreoptToolDepsMutator).Parallel()
 	})