diff --git a/clang/include/clang/AST/ASTVector.h b/clang/include/clang/AST/ASTVector.h
index 9ae5fd62c65a..717a9e9dff34 100644
--- a/clang/include/clang/AST/ASTVector.h
+++ b/clang/include/clang/AST/ASTVector.h
@@ -22,6 +22,7 @@
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/Support/type_traits.h"
 #include <algorithm>
+#include <cstddef>
 #include <cstring>
 #include <memory>