diff --git a/tools/build_rules/prelude_bazel b/tools/build_rules/prelude_bazel
index c0a8f55..5a600f2 100644
--- a/tools/build_rules/prelude_bazel
+++ b/tools/build_rules/prelude_bazel
@@ -1,3 +1,4 @@
+# -*- mode: bazel -*-
 # A global prelude for all BUILD[.bazel] files
 
 load("//tools/python:defs.bzl",