diff --git a/pybind11_protobuf/enum_type_caster.h b/pybind11_protobuf/enum_type_caster.h
index 5765233..d30369b 100644
--- a/pybind11_protobuf/enum_type_caster.h
+++ b/pybind11_protobuf/enum_type_caster.h
@@ -1,3 +1,8 @@
+// IWYU pragma: always_keep // Appears to be the best we can do at the moment.
+// What we really want (but does not work with Include Cleaner @ 2023-10-27):
+// * If native_proto_caster.h is included: suggest removing enum_type_caster.h
+// * If only enum_type_caster.h is included: always_keep
+
 #ifndef PYBIND11_PROTOBUF_ENUM_TYPE_CASTER_H_
 #define PYBIND11_PROTOBUF_ENUM_TYPE_CASTER_H_
 
diff --git a/pybind11_protobuf/native_proto_caster.h b/pybind11_protobuf/native_proto_caster.h
index bc4ca54..32afb50 100644
--- a/pybind11_protobuf/native_proto_caster.h
+++ b/pybind11_protobuf/native_proto_caster.h
@@ -1,3 +1,5 @@
+// IWYU pragma: always_keep // See pybind11/docs/type_caster_iwyu.rst
+
 #ifndef PYBIND11_PROTOBUF_NATIVE_PROTO_CASTERS_H_
 #define PYBIND11_PROTOBUF_NATIVE_PROTO_CASTERS_H_
 
diff --git a/pybind11_protobuf/proto_cast_util.h b/pybind11_protobuf/proto_cast_util.h
index 75c136c..4821e94 100644
--- a/pybind11_protobuf/proto_cast_util.h
+++ b/pybind11_protobuf/proto_cast_util.h
@@ -1,3 +1,5 @@
+// IWYU pragma: private, include "pybind11_protobuf/native_proto_caster.h"
+
 #ifndef PYBIND11_PROTOBUF_PROTO_CAST_UTIL_H_
 #define PYBIND11_PROTOBUF_PROTO_CAST_UTIL_H_
 
diff --git a/pybind11_protobuf/proto_caster_impl.h b/pybind11_protobuf/proto_caster_impl.h
index 3508ee6..f54b175 100644
--- a/pybind11_protobuf/proto_caster_impl.h
+++ b/pybind11_protobuf/proto_caster_impl.h
@@ -1,3 +1,5 @@
+// IWYU pragma: private, include "pybind11_protobuf/native_proto_caster.h"
+
 #ifndef PYBIND11_PROTOBUF_PROTO_CASTER_IMPL_H_
 #define PYBIND11_PROTOBUF_PROTO_CASTER_IMPL_H_
 
diff --git a/pybind11_protobuf/wrapped_proto_caster.h b/pybind11_protobuf/wrapped_proto_caster.h
index d45282f..18cf7da 100644
--- a/pybind11_protobuf/wrapped_proto_caster.h
+++ b/pybind11_protobuf/wrapped_proto_caster.h
@@ -1,3 +1,5 @@
+// IWYU pragma: always_keep // See pybind11/docs/type_caster_iwyu.rst
+
 #ifndef PYBIND11_PROTOBUF_WRAPPED_PROTO_CASTER_H_
 #define PYBIND11_PROTOBUF_WRAPPED_PROTO_CASTER_H_