diff --git a/curl/src/client.cc b/curl/src/client.cc

index 558db6d..d27bb36 100644

--- a/curl/src/client.cc

+++ b/curl/src/client.cc

@@ -1,3 +1,4 @@

+#include <cstddef>

 #include <leatherman/curl/client.hpp>

 #include <leatherman/curl/request.hpp>

 #include <leatherman/curl/response.hpp>

diff --git a/util/src/posix/scoped_descriptor.cc b/util/src/posix/scoped_descriptor.cc

index 6fd1495..8294d0b 100644

--- a/util/src/posix/scoped_descriptor.cc

+++ b/util/src/posix/scoped_descriptor.cc

@@ -1,3 +1,5 @@

+#include <cstddef>

+

 #include <leatherman/util/posix/scoped_descriptor.hpp>

 using namespace std;

diff --git a/util/src/scope_exit.cc b/util/src/scope_exit.cc

index 764c2fb..441855a 100644

--- a/util/src/scope_exit.cc

+++ b/util/src/scope_exit.cc

@@ -1,3 +1,4 @@

+#include <cstddef>

 #include <leatherman/util/scope_exit.hpp>

 using namespace std;

diff --git a/util/src/scoped_env.cc b/util/src/scoped_env.cc

index 6c6a041..df26645 100644

--- a/util/src/scoped_env.cc

+++ b/util/src/scoped_env.cc

@@ -1,3 +1,5 @@

+#include <cstddef>

+

 #include <leatherman/util/scoped_env.hpp>

 #include <leatherman/util/environment.hpp>