diff --git a/configure b/configure
index fb6a4914b06..04eeb1a741c 100755
--- a/configure
+++ b/configure
@@ -760,6 +760,7 @@ CLANG
 LLVM_CONFIG
 AWK
 with_llvm
+have_cxx
 ac_ct_CXX
 CXXFLAGS
 CXX
@@ -4769,6 +4770,13 @@ ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $
 ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
+if test -n "$ac_ct_CXX"; then
+  have_cxx=yes
+else
+  have_cxx=no
+fi
+
+
 # Check if it's Intel's compiler, which (usually) pretends to be gcc,
 # but has idiosyncrasies of its own.  We assume icc will define
 # __INTEL_COMPILER regardless of CFLAGS.
diff --git a/configure.ac b/configure.ac
index d3febfe58f1..13c75170f7a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -387,6 +387,13 @@ fi
 
 AC_PROG_CXX([$pgac_cxx_list])
 
+if test -n "$ac_ct_CXX"; then
+  have_cxx=yes
+else
+  have_cxx=no
+fi
+AC_SUBST(have_cxx)
+
 # Check if it's Intel's compiler, which (usually) pretends to be gcc,
 # but has idiosyncrasies of its own.  We assume icc will define
 # __INTEL_COMPILER regardless of CFLAGS.
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index 371cd7eba2c..947a2d79e29 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -280,6 +280,8 @@ PERMIT_DECLARATION_AFTER_STATEMENT = @PERMIT_DECLARATION_AFTER_STATEMENT@
 PERMIT_MISSING_VARIABLE_DECLARATIONS = @PERMIT_MISSING_VARIABLE_DECLARATIONS@
 CXXFLAGS = @CXXFLAGS@
 
+have_cxx = @have_cxx@
+
 LLVM_CPPFLAGS = @LLVM_CPPFLAGS@
 LLVM_CFLAGS = @LLVM_CFLAGS@
 LLVM_CXXFLAGS = @LLVM_CXXFLAGS@
diff --git a/src/makefiles/meson.build b/src/makefiles/meson.build
index aa2f9a87b14..77f7a729cc2 100644
--- a/src/makefiles/meson.build
+++ b/src/makefiles/meson.build
@@ -118,6 +118,8 @@ pgxs_kv = {
   'FLEXFLAGS': ' '.join(flex_flags),
 
   'LIBS': var_libs,
+
+  'have_cxx': have_cxx ? 'yes' : 'no',
 }
 
 if llvm.found()
diff --git a/src/test/modules/Makefile b/src/test/modules/Makefile
index 4c6d56d97d8..44c7163c1cd 100644
--- a/src/test/modules/Makefile
+++ b/src/test/modules/Makefile
@@ -75,5 +75,11 @@ else
 ALWAYS_SUBDIRS += ldap_password_func
 endif
 
+ifeq ($(have_cxx),yes)
+SUBDIRS += test_cplusplusext
+else
+ALWAYS_SUBDIRS += test_cplusplusext
+endif
+
 $(recurse)
 $(recurse_always)
diff --git a/src/test/modules/meson.build b/src/test/modules/meson.build
index 1b31c5b98d6..2634a519935 100644
--- a/src/test/modules/meson.build
+++ b/src/test/modules/meson.build
@@ -21,6 +21,7 @@ subdir('test_bitmapset')
 subdir('test_bloomfilter')
 subdir('test_cloexec')
 subdir('test_copy_callbacks')
+subdir('test_cplusplusext')
 subdir('test_custom_rmgrs')
 subdir('test_custom_stats')
 subdir('test_ddl_deparse')
diff --git a/src/test/modules/test_cplusplusext/.gitignore b/src/test/modules/test_cplusplusext/.gitignore
new file mode 100644
index 00000000000..913175ff6e6
--- /dev/null
+++ b/src/test/modules/test_cplusplusext/.gitignore
@@ -0,0 +1,3 @@
+/log/
+/results/
+/tmp_check/
diff --git a/src/test/modules/test_cplusplusext/Makefile b/src/test/modules/test_cplusplusext/Makefile
new file mode 100644
index 00000000000..88cd4403823
--- /dev/null
+++ b/src/test/modules/test_cplusplusext/Makefile
@@ -0,0 +1,26 @@
+# src/test/modules/test_cplusplusext/Makefile
+
+MODULE_big = test_cplusplusext
+OBJS = \
+	$(WIN32RES) \
+	test_cplusplusext.o
+PGFILEDESC = "test_cplusplusext - test C++ compatibility of PostgreSQL headers"
+
+EXTENSION = test_cplusplusext
+DATA = test_cplusplusext--1.0.sql
+
+REGRESS = test_cplusplusext
+
+# Use C++ compiler for linking because this module includes C++ files
+override COMPILER = $(CXX) $(CXXFLAGS)
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = src/test/modules/test_cplusplusext
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
diff --git a/src/test/modules/test_cplusplusext/README b/src/test/modules/test_cplusplusext/README
new file mode 100644
index 00000000000..8e4090edf01
--- /dev/null
+++ b/src/test/modules/test_cplusplusext/README
@@ -0,0 +1,10 @@
+test_cplusplusext - Test C++ Extension Compatibility
+====================================================
+
+This test module verifies that PostgreSQL headers and macros work
+correctly when compiled with a C++ compiler.
+
+While PostgreSQL already tests that headers are syntactically valid
+C++ using headerscheck, the macros defined in those headers might
+still expand to invalid C++ code.  This module catches such issues by
+actually compiling and running an extension that's written in C++.
diff --git a/src/test/modules/test_cplusplusext/expected/test_cplusplusext.out b/src/test/modules/test_cplusplusext/expected/test_cplusplusext.out
new file mode 100644
index 00000000000..ab0b04b5c5e
--- /dev/null
+++ b/src/test/modules/test_cplusplusext/expected/test_cplusplusext.out
@@ -0,0 +1,7 @@
+CREATE EXTENSION test_cplusplusext;
+SELECT test_cplusplus_add(1, 2);
+ test_cplusplus_add 
+--------------------
+                  3
+(1 row)
+
diff --git a/src/test/modules/test_cplusplusext/meson.build b/src/test/modules/test_cplusplusext/meson.build
new file mode 100644
index 00000000000..d13210ca593
--- /dev/null
+++ b/src/test/modules/test_cplusplusext/meson.build
@@ -0,0 +1,42 @@
+# Copyright (c) 2025-2026, PostgreSQL Global Development Group
+
+if not have_cxx
+  subdir_done()
+endif
+
+# Currently not supported, to be fixed.
+if cc.get_id() == 'msvc'
+  subdir_done()
+endif
+
+test_cplusplusext_sources = files(
+  'test_cplusplusext.cpp',
+)
+
+if host_system == 'windows'
+  test_cplusplusext_sources += rc_lib_gen.process(win32ver_rc, extra_args: [
+    '--NAME', 'test_cplusplusext',
+    '--FILEDESC', 'test_cplusplusext - test C++ compatibility of PostgreSQL headers',])
+endif
+
+test_cplusplusext = shared_module('test_cplusplusext',
+  test_cplusplusext_sources,
+  kwargs: pg_test_mod_args,
+)
+test_install_libs += test_cplusplusext
+
+test_install_data += files(
+  'test_cplusplusext.control',
+  'test_cplusplusext--1.0.sql',
+)
+
+tests += {
+  'name': 'test_cplusplusext',
+  'sd': meson.current_source_dir(),
+  'bd': meson.current_build_dir(),
+  'regress': {
+    'sql': [
+      'test_cplusplusext',
+    ],
+  },
+}
diff --git a/src/test/modules/test_cplusplusext/sql/test_cplusplusext.sql b/src/test/modules/test_cplusplusext/sql/test_cplusplusext.sql
new file mode 100644
index 00000000000..a41682417ae
--- /dev/null
+++ b/src/test/modules/test_cplusplusext/sql/test_cplusplusext.sql
@@ -0,0 +1,3 @@
+CREATE EXTENSION test_cplusplusext;
+
+SELECT test_cplusplus_add(1, 2);
diff --git a/src/test/modules/test_cplusplusext/test_cplusplusext--1.0.sql b/src/test/modules/test_cplusplusext/test_cplusplusext--1.0.sql
new file mode 100644
index 00000000000..c54acb76823
--- /dev/null
+++ b/src/test/modules/test_cplusplusext/test_cplusplusext--1.0.sql
@@ -0,0 +1,8 @@
+/* src/test/modules/test_cplusplusext/test_cplusplusext--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION test_cplusplusext" to load this file. \quit
+
+CREATE FUNCTION test_cplusplus_add(int4, int4) RETURNS int4
+AS 'MODULE_PATHNAME'
+LANGUAGE C STRICT;
diff --git a/src/test/modules/test_cplusplusext/test_cplusplusext.control b/src/test/modules/test_cplusplusext/test_cplusplusext.control
new file mode 100644
index 00000000000..640a0a51f35
--- /dev/null
+++ b/src/test/modules/test_cplusplusext/test_cplusplusext.control
@@ -0,0 +1,4 @@
+comment = 'Test module for C++ extension compatibility'
+default_version = '1.0'
+module_pathname = '$libdir/test_cplusplusext'
+relocatable = true
diff --git a/src/test/modules/test_cplusplusext/test_cplusplusext.cpp b/src/test/modules/test_cplusplusext/test_cplusplusext.cpp
new file mode 100644
index 00000000000..435937c00d2
--- /dev/null
+++ b/src/test/modules/test_cplusplusext/test_cplusplusext.cpp
@@ -0,0 +1,37 @@
+/*--------------------------------------------------------------------------
+ *
+ * test_cplusplusext.cpp
+ *		Test that PostgreSQL headers compile with a C++ compiler.
+ *
+ * This file is compiled with a C++ compiler to verify that PostgreSQL
+ * headers remain compatible with C++ extensions.
+ *
+ * Copyright (c) 2025-2026, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *		src/test/modules/test_cplusplusext/test_cplusplusext.cpp
+ *
+ * -------------------------------------------------------------------------
+ */
+
+extern "C" {
+#include "postgres.h"
+#include "fmgr.h"
+
+PG_MODULE_MAGIC;
+
+PG_FUNCTION_INFO_V1(test_cplusplus_add);
+}
+
+/*
+ * Simple function that returns the sum of two integers.  This verifies that
+ * C++ extension modules can be loaded and called correctly at runtime.
+ */
+extern "C" Datum
+test_cplusplus_add(PG_FUNCTION_ARGS)
+{
+	int32		a = PG_GETARG_INT32(0);
+	int32		b = PG_GETARG_INT32(1);
+
+	PG_RETURN_INT32(a + b);
+}