diff --git a/include/clap/helpers/host.hxx b/include/clap/helpers/host.hxx
index 13b3e33..428ebce 100644
--- a/include/clap/helpers/host.hxx
+++ b/include/clap/helpers/host.hxx
@@ -1,3 +1,5 @@
+#pragma once
+
 #include <cstring>
 #include <iostream>
 #include <sstream>
diff --git a/include/clap/helpers/note-end-queue.hh b/include/clap/helpers/note-end-queue.hh
index ed675b9..a13ea07 100644
--- a/include/clap/helpers/note-end-queue.hh
+++ b/include/clap/helpers/note-end-queue.hh
@@ -1,3 +1,5 @@
+#pragma once
+
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
diff --git a/include/clap/helpers/plugin-proxy.hxx b/include/clap/helpers/plugin-proxy.hxx
index e768639..c695eb1 100644
--- a/include/clap/helpers/plugin-proxy.hxx
+++ b/include/clap/helpers/plugin-proxy.hxx
@@ -1,3 +1,5 @@
+#pragma once
+
 #include <cassert>
 #include <sstream>
 
diff --git a/include/clap/helpers/plugin.hxx b/include/clap/helpers/plugin.hxx
index 3af46e7..c3ac627 100644
--- a/include/clap/helpers/plugin.hxx
+++ b/include/clap/helpers/plugin.hxx
@@ -1,3 +1,5 @@
+#pragma once
+
 #include <cassert>
 #include <cstring>
 #include <exception>