diff --git a/filesystem/filesystem.go b/filesystem/filesystem.go
index 4b4dc40..bff0a10 100644
--- a/filesystem/filesystem.go
+++ b/filesystem/filesystem.go
@@ -606,6 +606,7 @@
 		Input(propFile).
 		Implicits(toolDeps).
 		Implicit(fec).
+		FlagWithArg("--build_datetime_file ", ctx.Config().Getenv("BUILD_DATETIME_FILE")).
 		Output(output).
 		Text(rootDir.String()) // directory where to find fs_config_files|dirs