diff --git a/src/libexpr/primops.hh b/src/libexpr/primops.hh
index ed5e2ea58..9d42d6539 100644
--- a/src/libexpr/primops.hh
+++ b/src/libexpr/primops.hh
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "eval.hh"
 
 #include <tuple>
diff --git a/src/libstore/daemon.hh b/src/libstore/daemon.hh
index 841ace316..67755d54e 100644
--- a/src/libstore/daemon.hh
+++ b/src/libstore/daemon.hh
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "serialise.hh"
 #include "store-api.hh"
 
diff --git a/src/libstore/parsed-derivations.hh b/src/libstore/parsed-derivations.hh
index 3fa09f34f..c9fbe68c4 100644
--- a/src/libstore/parsed-derivations.hh
+++ b/src/libstore/parsed-derivations.hh
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "store-api.hh"
 
 #include <nlohmann/json_fwd.hpp>
diff --git a/src/libutil/topo-sort.hh b/src/libutil/topo-sort.hh
index 7a68ff169..7418be5e0 100644
--- a/src/libutil/topo-sort.hh
+++ b/src/libutil/topo-sort.hh
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "error.hh"
 
 namespace nix {