diff --git a/hpb/BUILD b/hpb/BUILD
index ad97ba856258f..d29e10fce78b6 100644
--- a/hpb/BUILD
+++ b/hpb/BUILD
@@ -187,14 +187,19 @@ cc_library(
         ":arena",
         ":multibackend",
         ":ptr",
-        "//hpb/backend/upb:extension",
-        "//hpb/backend/upb:interop",
         "//hpb/internal:message_lock",
         "//hpb/internal:template_help",
         "//upb/message",
         "//upb/mini_table",
         "@abseil-cpp//absl/base:core_headers",
-    ],
+    ] + select({
+        "//hpb:hpb_backend_cpp": [
+        ],
+        "//hpb:hpb_backend_upb": [
+            "//hpb/backend/upb:extension",
+            "//hpb/backend/upb:interop",
+        ],
+    }),
 )
 
 cc_library(
diff --git a/hpb/extension.h b/hpb/extension.h
index af1920d8a021f..5a58f7abd4e23 100644
--- a/hpb/extension.h
+++ b/hpb/extension.h
@@ -13,14 +13,16 @@
 
 #include "absl/base/attributes.h"
 #include "hpb/arena.h"
-#include "hpb/backend/upb/extension.h"
-#include "hpb/backend/upb/interop.h"
 #include "hpb/internal/message_lock.h"
 #include "hpb/internal/template_help.h"
 #include "hpb/multibackend.h"
 #include "hpb/ptr.h"
 #include "upb/message/accessors.h"
 #include "upb/mini_table/extension_registry.h"
+#if HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
+#include "hpb/backend/upb/extension.h"
+#include "hpb/backend/upb/interop.h"
+#endif  // HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
 
 namespace hpb {
 // upb has a notion of an ExtensionRegistry. We expect most callers to use
@@ -87,6 +89,7 @@ class ExtensionRegistry {
   explicit ExtensionRegistry() = default;
 };
 
+#if HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
 template <typename T, typename Extendee, typename Extension,
           typename = hpb::internal::EnableIfHpbClassThatHasExtensions<T>>
 ABSL_MUST_USE_RESULT bool HasExtension(
@@ -186,6 +189,7 @@ constexpr uint32_t ExtensionNumber(
     const internal::ExtensionIdentifier<T, Extension>& id) {
   return internal::PrivateAccess::GetExtensionNumber(id);
 }
+#endif  // HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
 
 }  // namespace hpb
 
diff --git a/hpb/internal/BUILD b/hpb/internal/BUILD
index 2c2336d161967..c70164fb9c529 100644
--- a/hpb/internal/BUILD
+++ b/hpb/internal/BUILD
@@ -49,6 +49,7 @@ cc_library(
         "//hpb:__subpackages__",
     ],
     deps = [
+        "//hpb:multibackend",
         "//upb/mem",
         "//upb/message",
     ],
diff --git a/hpb/internal/internal.h b/hpb/internal/internal.h
index f4be198ed4bd8..74fed915fbfd2 100644
--- a/hpb/internal/internal.h
+++ b/hpb/internal/internal.h
@@ -11,8 +11,12 @@
 #include <cstdint>
 #include <utility>
 
+#include "hpb/multibackend.h"
+
+#if HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
 #include "upb/mem/arena.h"
 #include "upb/message/message.h"
+#endif  // HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
 
 namespace hpb::internal {
 
@@ -25,6 +29,13 @@ struct PrivateAccess {
   static auto* GetInternalArena(T&& message) {
     return message->arena();
   }
+
+  template <typename T, typename... Args>
+  static constexpr auto InvokeConstructor(Args&&... args) {
+    return T(std::forward<Args>(args)...);
+  }
+
+#if HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
   template <typename T>
   static auto* GetInternalUPBArena(T&& arena) {
     return arena.arena_.ptr();
@@ -42,11 +53,6 @@ struct PrivateAccess {
     return typename T::Proxy(upb_Message_New(T::minitable(), arena), arena);
   }
 
-  template <typename T, typename... Args>
-  static constexpr auto InvokeConstructor(Args&&... args) {
-    return T(std::forward<Args>(args)...);
-  }
-
   template <typename ExtensionId>
   static constexpr uint32_t GetExtensionNumber(const ExtensionId& id) {
     return id.number();
@@ -56,10 +62,13 @@ struct PrivateAccess {
   static decltype(auto) GetDefaultValue(const ExtensionId& id) {
     return id.default_value();
   }
+#endif  // HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
 };
 
+#if HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
 template <typename T>
 struct AssociatedUpbTypes;
+#endif  // HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
 
 }  // namespace hpb::internal