diff --git a/src/google/protobuf/descriptor.h b/src/google/protobuf/descriptor.h
index 22bc03c745..c3be72bd34 100644
--- a/src/google/protobuf/descriptor.h
+++ b/src/google/protobuf/descriptor.h
@@ -769,6 +769,25 @@ class PROTOBUF_EXPORT FieldDescriptor : private internal::SymbolBase {
   // parse.
   bool requires_utf8_validation() const;
 
+  // Determines if the given enum field is treated as closed based on legacy
+  // non-conformant behavior.
+  //
+  // Conformant behavior determines closedness based on the enum and
+  // can be queried using EnumDescriptor::is_closed().
+  //
+  // Some runtimes currently have a quirk where non-closed enums are
+  // treated as closed when used as the type of fields defined in a
+  // `syntax = proto2;` file. This quirk is not present in all runtimes; as of
+  // writing, we know that:
+  //
+  // - C++, Java, and C++-based Python share this quirk.
+  // - UPB and UPB-based Python do not.
+  // - PHP and Ruby treat all enums as open regardless of declaration.
+  //
+  // Care should be taken when using this function to respect the target
+  // runtime's enum handling quirks.
+  bool legacy_enum_field_treated_as_closed() const;
+
   // Index of this field within the message's field array, or the file or
   // extension scope's extensions array.
   int index() const;
@@ -2443,6 +2462,11 @@ inline bool FieldDescriptor::requires_utf8_validation() const {
          file()->syntax() == FileDescriptor::SYNTAX_PROTO3;
 }
 
+inline bool FieldDescriptor::legacy_enum_field_treated_as_closed() const {
+  return type() == TYPE_ENUM &&
+         file()->syntax() == FileDescriptor::SYNTAX_PROTO2;
+}
+
 // To save space, index() is computed by looking at the descriptor's position
 // in the parent's array of children.
 inline int FieldDescriptor::index() const {
diff --git a/src/google/protobuf/descriptor_unittest.cc b/src/google/protobuf/descriptor_unittest.cc
index 64e6b2c52a..c4c7e933c0 100644
--- a/src/google/protobuf/descriptor_unittest.cc
+++ b/src/google/protobuf/descriptor_unittest.cc
@@ -1120,6 +1120,66 @@ TEST_F(DescriptorTest, NeedsUtf8Check) {
   EXPECT_FALSE(bar3->requires_utf8_validation());
 }
 
+TEST_F(DescriptorTest, EnumFieldTreatedAsClosed) {
+  // Make an open enum definition.
+  FileDescriptorProto open_enum_file;
+  open_enum_file.set_name("open_enum.proto");
+  open_enum_file.set_syntax("proto3");
+  AddEnumValue(AddEnum(&open_enum_file, "TestEnumOpen"), "TestEnumOpen_VALUE0",
+               0);
+
+  const EnumDescriptor* open_enum =
+      pool_.BuildFile(open_enum_file)->enum_type(0);
+  EXPECT_FALSE(open_enum->is_closed());
+
+  // Create a message that treats enum fields as closed.
+  FileDescriptorProto closed_file;
+  closed_file.set_name("closed_enum_field.proto");
+  closed_file.add_dependency("open_enum.proto");
+  closed_file.add_dependency("foo.proto");
+
+  DescriptorProto* message = AddMessage(&closed_file, "TestClosedEnumField");
+  AddField(message, "int_field", 1, FieldDescriptorProto::LABEL_OPTIONAL,
+           FieldDescriptorProto::TYPE_INT32);
+  AddField(message, "open_enum", 2, FieldDescriptorProto::LABEL_OPTIONAL,
+           FieldDescriptorProto::TYPE_ENUM)
+      ->set_type_name("TestEnumOpen");
+  AddField(message, "closed_enum", 3, FieldDescriptorProto::LABEL_OPTIONAL,
+           FieldDescriptorProto::TYPE_ENUM)
+      ->set_type_name("TestEnum");
+  const Descriptor* closed_message =
+      pool_.BuildFile(closed_file)->message_type(0);
+
+  EXPECT_FALSE(closed_message->FindFieldByName("int_field")
+                   ->legacy_enum_field_treated_as_closed());
+  EXPECT_TRUE(closed_message->FindFieldByName("closed_enum")
+                  ->legacy_enum_field_treated_as_closed());
+  EXPECT_TRUE(closed_message->FindFieldByName("open_enum")
+                  ->legacy_enum_field_treated_as_closed());
+}
+
+TEST_F(DescriptorTest, EnumFieldTreatedAsOpen) {
+  FileDescriptorProto open_enum_file;
+  open_enum_file.set_name("open_enum.proto");
+  open_enum_file.set_syntax("proto3");
+  AddEnumValue(AddEnum(&open_enum_file, "TestEnumOpen"), "TestEnumOpen_VALUE0",
+               0);
+  DescriptorProto* message = AddMessage(&open_enum_file, "TestOpenEnumField");
+  AddField(message, "int_field", 1, FieldDescriptorProto::LABEL_OPTIONAL,
+           FieldDescriptorProto::TYPE_INT32);
+  AddField(message, "open_enum", 2, FieldDescriptorProto::LABEL_OPTIONAL,
+           FieldDescriptorProto::TYPE_ENUM)
+      ->set_type_name("TestEnumOpen");
+  const FileDescriptor* open_enum_file_desc = pool_.BuildFile(open_enum_file);
+  const Descriptor* open_message = open_enum_file_desc->message_type(0);
+  const EnumDescriptor* open_enum = open_enum_file_desc->enum_type(0);
+  EXPECT_FALSE(open_enum->is_closed());
+  EXPECT_FALSE(open_message->FindFieldByName("int_field")
+                   ->legacy_enum_field_treated_as_closed());
+  EXPECT_FALSE(open_message->FindFieldByName("open_enum")
+                   ->legacy_enum_field_treated_as_closed());
+}
+
 TEST_F(DescriptorTest, IsMap) {
   EXPECT_TRUE(map_->is_map());
   EXPECT_FALSE(baz_->is_map());