diff --git a/src/google/protobuf/compiler/cpp/enum.cc b/src/google/protobuf/compiler/cpp/enum.cc
index a43106f6b2..e23d6e0d64 100644
--- a/src/google/protobuf/compiler/cpp/enum.cc
+++ b/src/google/protobuf/compiler/cpp/enum.cc
@@ -12,6 +12,7 @@
 #include "google/protobuf/compiler/cpp/enum.h"
 
 #include <algorithm>
+#include <cstddef>
 #include <cstdint>
 #include <limits>
 #include <string>