diff --git a/Include/internal/pycore_accu.h b/Include/internal/pycore_accu.h
index ab1aad2..4350db5 100644
--- a/Include/internal/pycore_accu.h
+++ b/Include/internal/pycore_accu.h
@@ -9,6 +9,10 @@
  *** Its definition may be changed or removed at any moment.
  ***/
 
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
+#endif
+
 /*
  * A two-level accumulator of unicode objects that avoids both the overhead
  * of keeping a huge number of small separate objects, and the quadratic
diff --git a/Include/internal/pycore_atomic.h b/Include/internal/pycore_atomic.h
index 5f349cc..f430a5c 100644
--- a/Include/internal/pycore_atomic.h
+++ b/Include/internal/pycore_atomic.h
@@ -4,8 +4,8 @@
 extern "C" {
 #endif
 
-#ifndef Py_BUILD_CORE
-#  error "Py_BUILD_CORE must be defined to include this header"
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
 #endif
 
 #include "dynamic_annotations.h"
diff --git a/Include/internal/pycore_ceval.h b/Include/internal/pycore_ceval.h
index ddeeb5c..c8c63b1 100644
--- a/Include/internal/pycore_ceval.h
+++ b/Include/internal/pycore_ceval.h
@@ -4,6 +4,10 @@
 extern "C" {
 #endif
 
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
+#endif
+
 #include "pycore_atomic.h"
 #include "pythread.h"
 
diff --git a/Include/internal/pycore_condvar.h b/Include/internal/pycore_condvar.h
index f933089..a12b699 100644
--- a/Include/internal/pycore_condvar.h
+++ b/Include/internal/pycore_condvar.h
@@ -1,6 +1,10 @@
 #ifndef Py_INTERNAL_CONDVAR_H
 #define Py_INTERNAL_CONDVAR_H
 
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
+#endif
+
 #ifndef _POSIX_THREADS
 /* This means pthreads are not implemented in libc headers, hence the macro
    not present in unistd.h. But they still can be implemented as an external
diff --git a/Include/internal/pycore_context.h b/Include/internal/pycore_context.h
index 57a410c..70701cd 100644
--- a/Include/internal/pycore_context.h
+++ b/Include/internal/pycore_context.h
@@ -1,10 +1,12 @@
 #ifndef Py_INTERNAL_CONTEXT_H
 #define Py_INTERNAL_CONTEXT_H
 
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
+#endif
 
 #include "pycore_hamt.h"
 
-
 struct _pycontextobject {
     PyObject_HEAD
     PyContext *ctx_prev;
@@ -37,5 +39,4 @@
 int _PyContext_Init(void);
 void _PyContext_Fini(void);
 
-
 #endif /* !Py_INTERNAL_CONTEXT_H */
diff --git a/Include/internal/pycore_getopt.h b/Include/internal/pycore_getopt.h
index 8ef2ada..e6f4654 100644
--- a/Include/internal/pycore_getopt.h
+++ b/Include/internal/pycore_getopt.h
@@ -1,6 +1,10 @@
 #ifndef Py_INTERNAL_PYGETOPT_H
 #define Py_INTERNAL_PYGETOPT_H
 
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
+#endif
+
 extern int _PyOS_opterr;
 extern int _PyOS_optind;
 extern wchar_t *_PyOS_optarg;
diff --git a/Include/internal/pycore_gil.h b/Include/internal/pycore_gil.h
index 5059850..014e75f 100644
--- a/Include/internal/pycore_gil.h
+++ b/Include/internal/pycore_gil.h
@@ -4,6 +4,10 @@
 extern "C" {
 #endif
 
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
+#endif
+
 #include "pycore_condvar.h"
 #include "pycore_atomic.h"
 
diff --git a/Include/internal/pycore_hamt.h b/Include/internal/pycore_hamt.h
index 29ad28b..8b2ce1f 100644
--- a/Include/internal/pycore_hamt.h
+++ b/Include/internal/pycore_hamt.h
@@ -1,6 +1,9 @@
 #ifndef Py_INTERNAL_HAMT_H
 #define Py_INTERNAL_HAMT_H
 
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
+#endif
 
 #define _Py_HAMT_MAX_TREE_DEPTH 7
 
diff --git a/Include/internal/pycore_hash.h b/Include/internal/pycore_hash.h
index e14b80a..babbc95 100644
--- a/Include/internal/pycore_hash.h
+++ b/Include/internal/pycore_hash.h
@@ -1,6 +1,10 @@
 #ifndef Py_INTERNAL_HASH_H
 #define Py_INTERNAL_HASH_H
 
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
+#endif
+
 uint64_t _Py_KeyedHash(uint64_t, const char *, Py_ssize_t);
 
 #endif
diff --git a/Include/internal/pycore_lifecycle.h b/Include/internal/pycore_lifecycle.h
index cf36440..e104316 100644
--- a/Include/internal/pycore_lifecycle.h
+++ b/Include/internal/pycore_lifecycle.h
@@ -4,8 +4,8 @@
 extern "C" {
 #endif
 
-#ifndef Py_BUILD_CORE
-#  error "Py_BUILD_CORE must be defined to include this header"
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
 #endif
 
 PyAPI_FUNC(int) _Py_UnixMain(int argc, char **argv);
diff --git a/Include/internal/pycore_mem.h b/Include/internal/pycore_mem.h
index 4a41b77..247426a 100644
--- a/Include/internal/pycore_mem.h
+++ b/Include/internal/pycore_mem.h
@@ -4,8 +4,8 @@
 extern "C" {
 #endif
 
-#ifndef Py_BUILD_CORE
-#  error "Py_BUILD_CORE must be defined to include this header"
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN defined"
 #endif
 
 #include "objimpl.h"
diff --git a/Include/internal/pycore_pathconfig.h b/Include/internal/pycore_pathconfig.h
index 00d7bbf..267e690 100644
--- a/Include/internal/pycore_pathconfig.h
+++ b/Include/internal/pycore_pathconfig.h
@@ -4,8 +4,8 @@
 extern "C" {
 #endif
 
-#ifndef Py_BUILD_CORE
-#  error "Py_BUILD_CORE must be defined to include this header"
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
 #endif
 
 PyAPI_FUNC(void) _Py_wstrlist_clear(
diff --git a/Include/internal/pycore_state.h b/Include/internal/pycore_state.h
index 6285ecf..01f2140 100644
--- a/Include/internal/pycore_state.h
+++ b/Include/internal/pycore_state.h
@@ -4,8 +4,8 @@
 extern "C" {
 #endif
 
-#ifndef Py_BUILD_CORE
-#  error "Py_BUILD_CORE must be defined to include this header"
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
 #endif
 
 #include "pystate.h"
diff --git a/Include/internal/pycore_warnings.h b/Include/internal/pycore_warnings.h
index 2878a28..91bf902 100644
--- a/Include/internal/pycore_warnings.h
+++ b/Include/internal/pycore_warnings.h
@@ -4,6 +4,10 @@
 extern "C" {
 #endif
 
+#if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
+#  error "this header requires Py_BUILD_CORE or Py_BUILD_CORE_BUILTIN define"
+#endif
+
 #include "object.h"
 
 struct _warnings_runtime_state {