--- a/pybind11_protobuf/BUILD
+++ b/pybind11_protobuf/BUILD
@@ -46,7 +46,6 @@
         "@com_google_absl//absl/strings",
         "@com_google_absl//absl/types:optional",
         "@com_google_protobuf//:protobuf",
-        "@com_google_protobuf//python:proto_api",
     ],
 )
 
@@ -75,7 +74,6 @@
         "@com_google_absl//absl/synchronization",
         "@com_google_absl//absl/types:optional",
         "@com_google_protobuf//:protobuf",
-        "@com_google_protobuf//python:proto_api",
     ],
 )
 
--- a/pybind11_protobuf/check_unknown_fields.h
+++ b/pybind11_protobuf/check_unknown_fields.h
@@ -6,7 +6,11 @@
 #include "absl/strings/string_view.h"
 #include "absl/types/optional.h"
 #include "google/protobuf/message.h"
+#if __has_include("python/google/protobuf/proto_api.h")
 #include "python/google/protobuf/proto_api.h"
+#else
+namespace google::protobuf::python { struct PyProto_API; }
+#endif
 
 namespace pybind11_protobuf::check_unknown_fields {
 
--- a/pybind11_protobuf/check_unknown_fields.cc
+++ b/pybind11_protobuf/check_unknown_fields.cc
@@ -15,7 +15,9 @@
 #include "google/protobuf/descriptor.h"
 #include "google/protobuf/message.h"
 #include "google/protobuf/unknown_field_set.h"
+#if __has_include("python/google/protobuf/proto_api.h")
 #include "python/google/protobuf/proto_api.h"
+#endif
 
 namespace pybind11_protobuf::check_unknown_fields {
 namespace {
@@ -103,11 +105,16 @@
     unknown_field_number = unknown_field_set.field(0).number();
 
     // Stop only if the extension is known by Python.
+#if __has_include("python/google/protobuf/proto_api.h")
     if (py_proto_api->GetDefaultDescriptorPool()->FindExtensionByNumber(
             unknown_field_parent_descriptor, unknown_field_number)) {
       field_fqn_parts.resize(depth);
       return true;
     }
+#else
+    field_fqn_parts.resize(depth);
+    return true;
+#endif
   }
 
   // If this message does not include submessages which allow extensions,
@@ -184,6 +191,9 @@
 absl::optional<std::string> CheckRecursively(
     const ::google::protobuf::python::PyProto_API* py_proto_api,
     const ::google::protobuf::Message* message) {
+#if !__has_include("python/google/protobuf/proto_api.h")
+  return absl::nullopt;
+#else
   const auto* root_descriptor = message->GetDescriptor();
   HasUnknownFields search{py_proto_api, root_descriptor};
   if (!search.FindUnknownFieldsRecursive(message, 0u)) {
@@ -194,6 +204,7 @@
     return absl::nullopt;
   }
   return search.BuildErrorMessage();
+#endif
 }
 
 }  // namespace pybind11_protobuf::check_unknown_fields