diff --git a/hpb/backend/BUILD b/hpb/backend/BUILD
index fc615dd4dc355..7f06107dd0286 100644
--- a/hpb/backend/BUILD
+++ b/hpb/backend/BUILD
@@ -5,6 +5,7 @@
 # license that can be found in the LICENSE file or at
 # https://developers.google.com/open-source/licenses/bsd
 
+load("@rules_cc//cc:cc_test.bzl", "cc_test")
 load("@rules_cc//cc:defs.bzl", "cc_library")
 
 package(default_applicable_licenses = ["//:license"])
@@ -26,3 +27,16 @@ cc_library(
         ],
     }),
 )
+
+cc_test(
+    name = "shared_test",
+    srcs = ["shared_test.cc"],
+    deps = [
+        "//hpb",
+        "//hpb:arena",
+        "//hpb:ptr",
+        "//hpb_generator/tests:test_model_hpb_proto",
+        "@googletest//:gtest",
+        "@googletest//:gtest_main",
+    ],
+)
diff --git a/hpb/backend/cpp/BUILD b/hpb/backend/cpp/BUILD
index 35a94e61166e2..4b0561956e2e7 100644
--- a/hpb/backend/cpp/BUILD
+++ b/hpb/backend/cpp/BUILD
@@ -5,7 +5,6 @@
 # license that can be found in the LICENSE file or at
 # https://developers.google.com/open-source/licenses/bsd
 
-load("@rules_cc//cc:cc_test.bzl", "cc_test")
 load("@rules_cc//cc:defs.bzl", "cc_library")
 
 package(default_applicable_licenses = ["//:license"])
@@ -43,16 +42,3 @@ cc_library(
     hdrs = ["repeated_field.h"],
     visibility = ["//hpb:__subpackages__"],
 )
-
-cc_test(
-    name = "cpp_test",
-    srcs = ["cpp_test.cc"],
-    deps = [
-        "//hpb",
-        "//hpb:arena",
-        "//hpb:ptr",
-        "//hpb_generator/tests:test_model_hpb_proto",
-        "@googletest//:gtest",
-        "@googletest//:gtest_main",
-    ],
-)
diff --git a/hpb/backend/cpp/cpp_test.cc b/hpb/backend/shared_test.cc
similarity index 68%
rename from hpb/backend/cpp/cpp_test.cc
rename to hpb/backend/shared_test.cc
index 6500249cd8c85..cc2060b2b9331 100644
--- a/hpb/backend/cpp/cpp_test.cc
+++ b/hpb/backend/shared_test.cc
@@ -15,11 +15,17 @@ namespace hpb::testing {
 namespace {
 
 using ::hpb_unittest::protos::TestModel;
+using ::hpb_unittest::protos::TestModel_Category_IMAGES;
 
-TEST(CppBackend, CanCreateMessage) {
+// Tests in this file are run against both backends {upb, cpp} to ensure
+// api conformance, compatibility, and correctness.
+
+TEST(MultiBackend, CanCreateMessage) {
   hpb::Arena arena;
   hpb::Ptr<TestModel> test_model_ptr = hpb::CreateMessage<TestModel>(arena);
   (void)test_model_ptr;
 }
+
+TEST(MultiBackend, MessageEnums) { EXPECT_EQ(5, TestModel_Category_IMAGES); }
 }  // namespace
 }  // namespace hpb::testing
diff --git a/hpb_generator/generator.cc b/hpb_generator/generator.cc
index f534ade7115b2..d93dac10ef8a4 100644
--- a/hpb_generator/generator.cc
+++ b/hpb_generator/generator.cc
@@ -57,6 +57,50 @@ void WriteForwardDecls(const google::protobuf::FileDescriptor* file, Context& ct
 void WriteHeader(const google::protobuf::FileDescriptor* file, Context& ctx) {
   if (ctx.options().backend == Backend::CPP) {
     EmitFileWarning(file, ctx);
+    ctx.Emit({{"filename", ToPreproc(file->name())}},
+             R"cc(
+#ifndef $filename$_HPB_PROTO_H_
+#define $filename$_HPB_PROTO_H_
+             )cc");
+
+    // Import headers for proto public dependencies.
+    for (int i = 0; i < file->public_dependency_count(); i++) {
+      if (i == 0) {
+        ctx.Emit("// Public Imports.\n");
+      }
+      ctx.Emit({{"header", CppHeaderFilename(file->public_dependency(i))}},
+               "#include \"$header$\"\n");
+      if (i == file->public_dependency_count() - 1) {
+        ctx.Emit("\n");
+      }
+    }
+
+    ctx.Emit(
+        "#include \"hpb/internal/os_macros_undef.inc\"\n");
+
+    const std::vector<const google::protobuf::Descriptor*> this_file_messages =
+        SortedMessages(file);
+    const std::vector<const google::protobuf::FieldDescriptor*>
+        this_file_exts{};  // TODO: extensions
+
+    if (!this_file_messages.empty()) {
+      ctx.Emit("\n");
+    }
+
+    WriteHeaderMessageForwardDecls(file, ctx);
+    WriteForwardDecls(file, ctx);
+
+    std::vector<const google::protobuf::EnumDescriptor*> this_file_enums =
+        SortedEnums(file);
+
+    WrapNamespace(file, ctx, [&]() {
+      // Write Class and Enums.
+      WriteEnumDeclarations(this_file_enums, ctx);
+      ctx.Emit("\n");
+      // TODO: class decls
+      // TODO: extension identifiers
+    });
+
     const auto msgs = SortedMessages(file);
     for (auto message : msgs) {
       ctx.Emit({{"type", QualifiedClassName(message)},
@@ -90,6 +134,11 @@ void WriteHeader(const google::protobuf::FileDescriptor* file, Context& ctx) {
                  }  // namespace $namespace$
                )cc");
     }
+    ctx.Emit(
+        "#include "
+        "\"hpb/internal/os_macros_restore.inc\"\n");
+    ctx.Emit({{"filename", ToPreproc(file->name())}},
+             "#endif  /* $filename$_HPB_PROTO_H_ */\n");
     return;
   }
   EmitFileWarning(file, ctx);
@@ -254,8 +303,10 @@ void WriteTypedefForwardingHeader(
 void WriteHeaderMessageForwardDecls(const google::protobuf::FileDescriptor* file,
                                     Context& ctx) {
   // Import forward-declaration of types defined in this file.
-  ctx.Emit({{"upb_filename", UpbCFilename(file)}},
-           "#include \"$upb_filename$\"\n");
+  if (ctx.options().backend == Backend::UPB) {
+    ctx.Emit({{"upb_filename", UpbCFilename(file)}},
+             "#include \"$upb_filename$\"\n");
+  }
   WriteForwardDecls(file, ctx);
   // Import forward-declaration of types in dependencies.
   for (int i = 0; i < file->dependency_count(); ++i) {