diff --git a/hpb_generator/context.h b/hpb_generator/context.h
index d7a7ae9bb0..f1e989fb62 100644
--- a/hpb_generator/context.h
+++ b/hpb_generator/context.h
@@ -9,7 +9,6 @@
 #define GOOGLE_PROTOBUF_COMPILER_HPB_CONTEXT_H__
 
 #include <string>
-#include <utility>
 
 #include "absl/strings/ascii.h"
 #include "absl/strings/str_cat.h"
@@ -21,7 +20,9 @@
 #include "google/protobuf/descriptor.h"
 #include "google/protobuf/io/printer.h"
 #include "google/protobuf/io/zero_copy_stream.h"
-#include "upb_generator/c/names.h"
+#include "upb/reflection/def.hpp"
+#include "upb_generator/common/cpp_to_upb_def.h"
+
 namespace google::protobuf::hpb_generator {
 
 enum class Backend { UPB, CPP };
@@ -44,8 +45,11 @@ struct Options {
  */
 class Context final {
  public:
-  Context(io::ZeroCopyOutputStream* stream, const Options& options)
-      : stream_(stream), printer_(stream_), options_(options) {}
+  Context(const FileDescriptor* file, io::ZeroCopyOutputStream* stream,
+          const Options& options)
+      : stream_(stream), printer_(stream_), options_(options) {
+    BuildDefPool(file);
+  }
 
   void Emit(absl::Span<const io::Printer::Sub> vars, absl::string_view format,
             absl::SourceLocation loc = absl::SourceLocation::current()) {
@@ -68,15 +72,25 @@ class Context final {
   const Options& options() { return options_; }
   io::Printer& printer() { return printer_; }
 
+  inline std::string GetLayoutIndex(const FieldDescriptor* field) {
+    return absl::StrCat(
+        upb::generator::FindBaseFieldDef(pool_, field).layout_index());
+  }
+
   Context(const Context&) = delete;
   Context& operator=(const Context&) = delete;
   Context(Context&&) = delete;
   Context& operator=(Context&&) = delete;
 
  private:
+  inline void BuildDefPool(const FileDescriptor* file) {
+    upb::generator::AddFile(file, &pool_);
+  }
+
   io::ZeroCopyOutputStream* stream_;
   io::Printer printer_;
   const Options& options_;
+  upb::DefPool pool_;
 };
 
 // TODO: b/373438292 - re-house these 4 legacy funcs post io::Printer move
diff --git a/hpb_generator/gen_accessors.cc b/hpb_generator/gen_accessors.cc
index d038374963..d480c85265 100644
--- a/hpb_generator/gen_accessors.cc
+++ b/hpb_generator/gen_accessors.cc
@@ -286,7 +286,7 @@ void WriteAccessorsInSource(const protobuf::Descriptor* desc, Context& ctx) {
                 ABSL_CHECK(upb_Arena_IsFused(arena_, hpb::interop::upb::GetArena(target)));
                 upb_Message_SetBaseFieldMessage(
                     UPB_UPCAST(msg_),
-                    upb_MiniTable_FindFieldByNumber($7::minitable(), $8),
+                    upb_MiniTable_GetFieldByIndex($7::minitable(), $8),
                     hpb::interop::upb::GetMessage(target));
               }
             )cc",
@@ -294,7 +294,7 @@ void WriteAccessorsInSource(const protobuf::Descriptor* desc, Context& ctx) {
             resolved_field_name,
             upb::generator::CApiMessageType(desc->full_name()),
             MessageBaseType(field, /* maybe_const */ false), resolved_upbc_name,
-            arena_expression, ClassName(desc), field->number());
+            arena_expression, ClassName(desc), ctx.GetLayoutIndex(field));
       }
     }
   }
diff --git a/hpb_generator/protoc-gen-hpb.cc b/hpb_generator/protoc-gen-hpb.cc
index 30d6b4e31e..e7cb0f0a6e 100644
--- a/hpb_generator/protoc-gen-hpb.cc
+++ b/hpb_generator/protoc-gen-hpb.cc
@@ -81,20 +81,22 @@ bool Generator::Generate(const protobuf::FileDescriptor* file,
   // Write model.upb.fwd.h
   std::unique_ptr<google::protobuf::io::ZeroCopyOutputStream> output_stream(
       context->Open(ForwardingHeaderFilename(file)));
-  auto fwd_ctx = Context(output_stream.get(), Options{.backend = Backend::UPB});
+  Context fwd_ctx =
+      Context(file, output_stream.get(), Options{.backend = Backend::UPB});
   WriteForwardingHeader(file, fwd_ctx);
 
   // Write model.upb.proto.h
   std::unique_ptr<google::protobuf::io::ZeroCopyOutputStream> header_output_stream(
       context->Open(CppHeaderFilename(file)));
-  Context hdr_ctx(header_output_stream.get(), Options{.backend = Backend::UPB});
+  Context hdr_ctx(file, header_output_stream.get(),
+                  Options{.backend = Backend::UPB});
   WriteHeader(file, hdr_ctx, strip_nonfunctional_codegen);
 
   // Write model.upb.proto.cc
   std::unique_ptr<google::protobuf::io::ZeroCopyOutputStream> cc_output_stream(
       context->Open(CppSourceFilename(file)));
   auto cc_ctx =
-      Context(cc_output_stream.get(), Options{.backend = Backend::UPB});
+      Context(file, cc_output_stream.get(), Options{.backend = Backend::UPB});
   WriteSource(file, cc_ctx, fasttable_enabled, strip_nonfunctional_codegen);
   return true;
 }