diff --git a/java/droiddoc.go b/java/droiddoc.go
index fd4b90d..5437499 100644
--- a/java/droiddoc.go
+++ b/java/droiddoc.go
@@ -773,6 +773,7 @@
 }
 
 func (d *Droiddoc) doclavaDocsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand, docletPath classpath) {
+	buildNumberFile := ctx.Config().BuildNumberFile(ctx)
 	// Droiddoc always gets "-source 1.8" because it doesn't support 1.9 sources.  For modules with 1.9
 	// sources, droiddoc will get sources produced by metalava which will have already stripped out the
 	// 1.9 language features.
@@ -782,7 +783,7 @@
 		Flag("-XDignore.symbol.file").
 		FlagWithArg("-doclet ", "com.google.doclava.Doclava").
 		FlagWithInputList("-docletpath ", docletPath.Paths(), ":").
-		FlagWithArg("-hdf page.build ", ctx.Config().BuildId()+"-"+ctx.Config().BuildNumberFromFile()).
+		FlagWithArg("-hdf page.build ", ctx.Config().BuildId()+"-$(cat "+buildNumberFile.String()+")").OrderOnly(buildNumberFile).
 		FlagWithArg("-hdf page.now ", `"$(date -d @$(cat `+ctx.Config().Getenv("BUILD_DATETIME_FILE")+`) "+%d %b %Y %k:%M")" `)
 
 	if String(d.properties.Custom_template) == "" {