diff --git a/third_party/libcxx/stdfloat b/third_party/libcxx/stdfloat
index 4126b4a8c..a3a27dcb5 100644
--- a/third_party/libcxx/stdfloat
+++ b/third_party/libcxx/stdfloat
@@ -1,4 +1,5 @@
 // -*- C++ -*-
+#pragma once
 
 export namespace std {