https://github.com/protobuf-c/protobuf-c/pull/711

Index: protoc-c/c_file.cc
--- protoc-c/c_file.cc.orig
+++ protoc-c/c_file.cc
@@ -117,14 +117,7 @@ FileGenerator::~FileGenerator() {}
 void FileGenerator::GenerateHeader(io::Printer* printer) {
   std::string filename_identifier = FilenameIdentifier(file_->name());
 
-  int min_header_version = 1000000;
-#if GOOGLE_PROTOBUF_VERSION >= 4023000
-  if (FileDescriptorLegacy(file_).syntax() == FileDescriptorLegacy::SYNTAX_PROTO3) {
-#else
-  if (file_->syntax() == FileDescriptor::SYNTAX_PROTO3) {
-#endif
-    min_header_version = 1003000;
-  }
+  const int min_header_version = 1003000;
 
   // Generate top of header.
   printer->Print(
