diff --git a/src/callback.hpp b/src/callback.hpp
index b1c8d0b..099cd7c 100644
--- a/src/callback.hpp
+++ b/src/callback.hpp
@@ -3,6 +3,7 @@
 #include "data_types.hpp"
 
 #include <chrono>
+#include <cstddef>
 #include <sdeventplus/clock.hpp>
 #include <sdeventplus/event.hpp>
 #include <sdeventplus/utility/timer.hpp>
diff --git a/src/count.hpp b/src/count.hpp
index 3e18e20..f231f26 100644
--- a/src/count.hpp
+++ b/src/count.hpp
@@ -4,6 +4,7 @@
 #include "data_types.hpp"
 
 #include <algorithm>
+#include <cstddef>
 #include <functional>
 
 namespace phosphor
diff --git a/src/tupleref.hpp b/src/tupleref.hpp
index 18bd7f4..3954d46 100644
--- a/src/tupleref.hpp
+++ b/src/tupleref.hpp
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <cstddef>
 #include <tuple>
 #include <utility>