diff --git a/Source/CPack/IFW/cmCPackIFWCommon.cxx b/Source/CPack/IFW/cmCPackIFWCommon.cxx
index f9ce822c2b..aa9a4572c6 100644
--- a/Source/CPack/IFW/cmCPackIFWCommon.cxx
+++ b/Source/CPack/IFW/cmCPackIFWCommon.cxx
@@ -11,6 +11,7 @@
 #include "cmVersionConfig.h"
 #include "cmXMLWriter.h"
 
+#include <cstddef>
 #include <sstream>
 #include <utility>
 #include <vector>
diff --git a/Source/CTest/cmCTestTestHandler.cxx b/Source/CTest/cmCTestTestHandler.cxx
index 547d2f3c0d..b90209edd4 100644
--- a/Source/CTest/cmCTestTestHandler.cxx
+++ b/Source/CTest/cmCTestTestHandler.cxx
@@ -28,6 +28,7 @@
 #include <cmsys/Base64.h>
 #include <cmsys/Directory.hxx>
 #include <cmsys/RegularExpression.hxx>
+#include <cstddef>
 #include <cstring>
 #include <functional>
 #include <iomanip>
diff --git a/Source/cmFileAPI.cxx b/Source/cmFileAPI.cxx
index 5d9181a7e7..8161191469 100644
--- a/Source/cmFileAPI.cxx
+++ b/Source/cmFileAPI.cxx
@@ -17,6 +17,7 @@
 #include <algorithm>
 #include <cassert>
 #include <chrono>
+#include <cstddef>
 #include <ctime>
 #include <iomanip>
 #include <sstream>
diff --git a/Source/cmGeneratorTarget.cxx b/Source/cmGeneratorTarget.cxx
index b9a9204496..8896e153ca 100644
--- a/Source/cmGeneratorTarget.cxx
+++ b/Source/cmGeneratorTarget.cxx
@@ -5,6 +5,7 @@
 #include "cmsys/RegularExpression.hxx"
 #include <algorithm>
 #include <assert.h>
+#include <cstddef>
 #include <errno.h>
 #include <iterator>
 #include <memory>
diff --git a/Source/cmListCommand.cxx b/Source/cmListCommand.cxx
index 91dea5870e..d2c051eae4 100644
--- a/Source/cmListCommand.cxx
+++ b/Source/cmListCommand.cxx
@@ -5,6 +5,7 @@
 #include "cmsys/RegularExpression.hxx"
 #include <algorithm>
 #include <assert.h>
+#include <cstddef>
 #include <functional>
 #include <iterator>
 #include <set>
diff --git a/Source/cmProjectCommand.cxx b/Source/cmProjectCommand.cxx
index f8c5adad8d..e74fff61eb 100644
--- a/Source/cmProjectCommand.cxx
+++ b/Source/cmProjectCommand.cxx
@@ -4,6 +4,7 @@
 
 #include "cmsys/RegularExpression.hxx"
 #include <array>
+#include <cstddef>
 #include <cstdio>
 #include <functional>
 #include <limits>
diff --git a/Source/cmQtAutoGenInitializer.cxx b/Source/cmQtAutoGenInitializer.cxx
index 155167b103..d6916b06b4 100644
--- a/Source/cmQtAutoGenInitializer.cxx
+++ b/Source/cmQtAutoGenInitializer.cxx
@@ -29,6 +29,7 @@
 #include "cmsys/SystemInformation.hxx"
 
 #include <algorithm>
+#include <cstddef>
 #include <deque>
 #include <initializer_list>
 #include <map>
diff --git a/Source/cmString.hxx b/Source/cmString.hxx
index 49bad78704..226ac67b22 100644
--- a/Source/cmString.hxx
+++ b/Source/cmString.hxx
@@ -9,6 +9,7 @@
 #include "cm_string_view.hxx"
 
 #include <algorithm>
+#include <cstddef>
 #include <functional>
 #include <initializer_list>
 #include <memory>
diff --git a/Source/cmStringAlgorithms.cxx b/Source/cmStringAlgorithms.cxx
index c686aa0134..131a01ecf5 100644
--- a/Source/cmStringAlgorithms.cxx
+++ b/Source/cmStringAlgorithms.cxx
@@ -3,6 +3,7 @@
 #include "cmStringAlgorithms.h"
 
 #include <algorithm>
+#include <cstddef>
 #include <cstdio>
 #include <errno.h>
 #include <stdlib.h>
diff --git a/Source/cmUVProcessChain.h b/Source/cmUVProcessChain.h
index 75f8f6623c..76a9c40cb0 100644
--- a/Source/cmUVProcessChain.h
+++ b/Source/cmUVProcessChain.h
@@ -6,6 +6,7 @@
 #include "cm_uv.h"
 
 #include <array>
+#include <cstddef>
 #include <iosfwd>
 #include <memory>
 #include <string>
diff --git a/Source/cmXMLWriter.h b/Source/cmXMLWriter.h
index 512e1031dc..a5b06af9f8 100644
--- a/Source/cmXMLWriter.h
+++ b/Source/cmXMLWriter.h
@@ -8,6 +8,7 @@
 #include "cmXMLSafe.h"
 
 #include <chrono>
+#include <cstddef>
 #include <ctime>
 #include <ostream>
 #include <stack>
diff --git a/Tests/CMakeLib/testString.cxx b/Tests/CMakeLib/testString.cxx
index af5e41ed31..075892f39f 100644
--- a/Tests/CMakeLib/testString.cxx
+++ b/Tests/CMakeLib/testString.cxx
@@ -6,6 +6,7 @@
 #include "cm_static_string_view.hxx"
 #include "cm_string_view.hxx"
 
+#include <cstddef>
 #include <cstring>
 #include <iostream>
 #include <iterator>