diff --git a/src/google/protobuf/compiler/csharp/csharp_helpers.cc b/src/google/protobuf/compiler/csharp/csharp_helpers.cc
index f15c5a2adb..a52599533c 100644
--- a/src/google/protobuf/compiler/csharp/csharp_helpers.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_helpers.cc
@@ -41,10 +41,12 @@
 
 #include <google/protobuf/wire_format.h>
 #include <google/protobuf/stubs/strutil.h>
+#include "absl/container/flat_hash_set.h"
 #include "absl/strings/ascii.h"
 #include "absl/strings/escaping.h"
 #include "absl/strings/str_replace.h"
 #include "absl/strings/str_split.h"
+#include "absl/strings/string_view.h"
 #include <google/protobuf/compiler/csharp/csharp_enum_field.h>
 #include <google/protobuf/compiler/csharp/csharp_field_base.h>
 #include <google/protobuf/compiler/csharp/csharp_map_field.h>