diff --git a/include/pybind11/detail/common.h b/include/pybind11/detail/common.h
index d1cf8bd956..ab6221aff4 100644
--- a/include/pybind11/detail/common.h
+++ b/include/pybind11/detail/common.h
@@ -50,6 +50,21 @@
 #    endif
 #endif
 
+// These PYBIND11_HAS_... macros are consolidated in pybind11/detail/common.h
+// to simplify backward compatibility handling for users (e.g., via #ifdef checks):
+#define PYBIND11_HAS_TYPE_CASTER_STD_FUNCTION_SPECIALIZATIONS 1
+#define PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT 1
+#define PYBIND11_HAS_CPP_CONDUIT 1
+#define PYBIND11_HAS_NATIVE_ENUM 1
+
+#if defined(PYBIND11_CPP17) && defined(__has_include)
+#    if __has_include(<filesystem>)
+#        define PYBIND11_HAS_FILESYSTEM 1
+#    elif __has_include(<experimental/filesystem>)
+#        define PYBIND11_HAS_EXPERIMENTAL_FILESYSTEM 1
+#    endif
+#endif
+
 #if defined(__cpp_lib_launder) && !(defined(_MSC_VER) && (_MSC_VER < 1914))
 #    define PYBIND11_STD_LAUNDER std::launder
 #    define PYBIND11_HAS_STD_LAUNDER 1
@@ -168,14 +183,9 @@
 #    define PYBIND11_HAS_VARIANT 1
 #endif
 
-#if defined(PYBIND11_CPP17)
-#    if defined(__has_include)
-#        if __has_include(<string_view>)
-#            define PYBIND11_HAS_STRING_VIEW
-#        endif
-#    elif defined(_MSC_VER)
-#        define PYBIND11_HAS_STRING_VIEW
-#    endif
+#if defined(PYBIND11_CPP17)                                                                       \
+    && ((defined(__has_include) && __has_include(<string_view>)) || defined(_MSC_VER))
+#    define PYBIND11_HAS_STRING_VIEW 1
 #endif
 
 #if (defined(PYPY_VERSION) || defined(GRAALVM_PYTHON)) && !defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
@@ -213,7 +223,7 @@
 
 // Must be after including <version> or one of the other headers specified by the standard
 #if defined(__cpp_lib_char8_t) && __cpp_lib_char8_t >= 201811L
-#    define PYBIND11_HAS_U8STRING
+#    define PYBIND11_HAS_U8STRING 1
 #endif
 
 // See description of PR #4246:
diff --git a/include/pybind11/detail/cpp_conduit.h b/include/pybind11/detail/cpp_conduit.h
index b66c2d39c0..a06b9b21a0 100644
--- a/include/pybind11/detail/cpp_conduit.h
+++ b/include/pybind11/detail/cpp_conduit.h
@@ -71,7 +71,5 @@ inline void *try_raw_pointer_ephemeral_from_cpp_conduit(handle src,
     return nullptr;
 }
 
-#define PYBIND11_HAS_CPP_CONDUIT 1
-
 PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
diff --git a/include/pybind11/detail/internals.h b/include/pybind11/detail/internals.h
index 5317695859..3687b48744 100644
--- a/include/pybind11/detail/internals.h
+++ b/include/pybind11/detail/internals.h
@@ -206,9 +206,6 @@ struct internals {
     }
 };
 
-// For backwards compatibility (i.e. #ifdef guards):
-#define PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
-
 enum class holder_enum_t : uint8_t {
     undefined,
     std_unique_ptr, // Default, lacking interop with std::shared_ptr.
diff --git a/include/pybind11/detail/native_enum_data.h b/include/pybind11/detail/native_enum_data.h
index 26aa965989..a8f7675ba0 100644
--- a/include/pybind11/detail/native_enum_data.h
+++ b/include/pybind11/detail/native_enum_data.h
@@ -4,8 +4,6 @@
 
 #pragma once
 
-#define PYBIND11_HAS_NATIVE_ENUM
-
 #include "../pytypes.h"
 #include "common.h"
 #include "internals.h"
diff --git a/include/pybind11/functional.h b/include/pybind11/functional.h
index 77ddf290ef..85f9b7907d 100644
--- a/include/pybind11/functional.h
+++ b/include/pybind11/functional.h
@@ -9,8 +9,6 @@
 
 #pragma once
 
-#define PYBIND11_HAS_TYPE_CASTER_STD_FUNCTION_SPECIALIZATIONS
-
 #include "pybind11.h"
 
 #include <functional>
diff --git a/include/pybind11/stl/filesystem.h b/include/pybind11/stl/filesystem.h
index fb8164e0d5..4246518809 100644
--- a/include/pybind11/stl/filesystem.h
+++ b/include/pybind11/stl/filesystem.h
@@ -12,22 +12,12 @@
 
 #include <string>
 
-#ifdef __has_include
-#    if defined(PYBIND11_CPP17)
-#        if __has_include(<filesystem>)
-#            include <filesystem>
-#            define PYBIND11_HAS_FILESYSTEM 1
-#        elif __has_include(<experimental/filesystem>)
-#            include <experimental/filesystem>
-#            define PYBIND11_HAS_EXPERIMENTAL_FILESYSTEM 1
-#        endif
-#    endif
-#endif
-
-#if !defined(PYBIND11_HAS_FILESYSTEM) && !defined(PYBIND11_HAS_EXPERIMENTAL_FILESYSTEM)           \
-    && !defined(PYBIND11_HAS_FILESYSTEM_IS_OPTIONAL)
-#    error                                                                                        \
-        "Neither #include <filesystem> nor #include <experimental/filesystem is available. (Use -DPYBIND11_HAS_FILESYSTEM_IS_OPTIONAL to ignore.)"
+#if defined(PYBIND11_HAS_FILESYSTEM)
+#    include <filesystem>
+#elif defined(PYBIND11_HAS_EXPERIMENTAL_FILESYSTEM)
+#    include <experimental/filesystem>
+#else
+#    error "Neither #include <filesystem> nor #include <experimental/filesystem is available."
 #endif
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
diff --git a/tests/test_stl.cpp b/tests/test_stl.cpp
index 5eff4f5838..5e6d6a333f 100644
--- a/tests/test_stl.cpp
+++ b/tests/test_stl.cpp
@@ -12,10 +12,10 @@
 #include "constructor_stats.h"
 #include "pybind11_tests.h"
 
-#ifndef PYBIND11_HAS_FILESYSTEM_IS_OPTIONAL
-#    define PYBIND11_HAS_FILESYSTEM_IS_OPTIONAL
+#if defined(PYBIND11_HAS_FILESYSTEM) || defined(PYBIND11_HAS_EXPERIMENTAL_FILESYSTEM)
+#    include <pybind11/stl/filesystem.h>
 #endif
-#include <pybind11/stl/filesystem.h>
+
 #include <pybind11/typing.h>
 
 #include <string>