diff --git a/ui/build/build.go b/ui/build/build.go
index 9650eaa..076e15e 100644
--- a/ui/build/build.go
+++ b/ui/build/build.go
@@ -32,6 +32,7 @@
 	// The ninja_build file is used by our buildbots to understand that the output
 	// can be parsed as ninja output.
 	ensureEmptyFileExists(ctx, filepath.Join(config.OutDir(), "ninja_build"))
+	ensureEmptyFileExists(ctx, filepath.Join(config.OutDir(), ".out-dir"))
 }
 
 var combinedBuildNinjaTemplate = template.Must(template.New("combined").Parse(`