diff --git a/include/ircd/util/scope_light.h b/include/ircd/util/scope_light.h
new file mode 100644
index 000000000..4a1b0923f
--- /dev/null
+++ b/include/ircd/util/scope_light.h
@@ -0,0 +1,48 @@
+// Matrix Construct
+//
+// Copyright (C) Matrix Construct Developers, Authors & Contributors
+// Copyright (C) 2016-2019 Jason Volk <jason@zemos.net>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice is present in all copies. The
+// full license for this software is available in the LICENSE file.
+
+#pragma once
+#define HAVE_IRCD_UTIL_SCOPE_LIGHT_H
+
+namespace ircd::util
+{
+	struct scope_light;
+};
+
+/// A simple boiler-plate  for setting a bool to true when constructed and
+/// resetting it to its previous value when destructed. This takes a runtime
+/// reference to that bool. This is not intended to be a replacement for the
+/// reentrance_assertion utility or ctx::mutex et al.
+struct ircd::util::scope_light
+{
+	bool *light {nullptr};
+	bool theirs {false};
+
+	scope_light(bool &light);
+	scope_light(const scope_light &) = delete;
+	scope_light(scope_light &&) noexcept = delete;
+	~scope_light() noexcept;
+};
+
+inline
+ircd::util::scope_light::scope_light(bool &light)
+:light{&light}
+,theirs{light}
+{
+	light = true;
+}
+
+inline
+ircd::util::scope_light::~scope_light()
+noexcept
+{
+	assert(light);
+	*light = theirs;
+}
diff --git a/include/ircd/util/util.h b/include/ircd/util/util.h
index 471229655..57c134a00 100644
--- a/include/ircd/util/util.h
+++ b/include/ircd/util/util.h
@@ -45,6 +45,7 @@ namespace ircd
 #include "bswap.h"
 #include "tuple.h"
 #include "timer.h"
+#include "scope_light.h"
 #include "life_guard.h"
 #include "pubsetbuf.h"
 #include "string.h"