diff --git a/inst/include/cpp11/environment.hpp b/inst/include/cpp11/environment.hpp
index 662e0995..159e4b89 100644
--- a/inst/include/cpp11/environment.hpp
+++ b/inst/include/cpp11/environment.hpp
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "cpp11/as.hpp"
 #include "cpp11/sexp.hpp"  // for sexp
 
diff --git a/inst/include/cpp11/external_pointer.hpp b/inst/include/cpp11/external_pointer.hpp
index 04452c9e..478b3aa3 100644
--- a/inst/include/cpp11/external_pointer.hpp
+++ b/inst/include/cpp11/external_pointer.hpp
@@ -1,3 +1,5 @@
+#pragma once
+
 #include <cstddef>
 #include <memory>
 #include "cpp11/sexp.hpp"
diff --git a/inst/include/cpp11/list_of.hpp b/inst/include/cpp11/list_of.hpp
index a5585fcf..62de4875 100644
--- a/inst/include/cpp11/list_of.hpp
+++ b/inst/include/cpp11/list_of.hpp
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "cpp11/list.hpp"
 
 namespace cpp11 {