diff --git a/libcxx/include/cctype b/libcxx/include/cctype
--- a/libcxx/include/cctype
+++ b/libcxx/include/cctype
@@ -36,8 +36,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <ctype.h>
 
+#ifndef _LIBCPP_CTYPE_H
+#   error "<cctype> tried including <ctype.h> but didn't find libc++'s <ctype.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cerrno b/libcxx/include/cerrno
--- a/libcxx/include/cerrno
+++ b/libcxx/include/cerrno
@@ -24,8 +24,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <errno.h>
 
+#ifndef _LIBCPP_ERRNO_H
+#   error "<cerrno> tried including <errno.h> but didn't find libc++'s <errno.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cfenv b/libcxx/include/cfenv
--- a/libcxx/include/cfenv
+++ b/libcxx/include/cfenv
@@ -54,8 +54,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <fenv.h>
 
+#ifndef _LIBCPP_FENV_H
+#   error "<cfenv> tried including <fenv.h> but didn't find libc++'s <fenv.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cfloat b/libcxx/include/cfloat
--- a/libcxx/include/cfloat
+++ b/libcxx/include/cfloat
@@ -71,8 +71,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <float.h>
 
+#ifndef _LIBCPP_FLOAT_H
+#   error "<cfloat> tried including <float.h> but didn't find libc++'s <float.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cinttypes b/libcxx/include/cinttypes
--- a/libcxx/include/cinttypes
+++ b/libcxx/include/cinttypes
@@ -237,8 +237,16 @@
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
 #include <cstdint>
+
 #include <inttypes.h>
 
+#ifndef _LIBCPP_INTTYPES_H
+#   error "<cinttypes> tried including <inttypes.h> but didn't find libc++'s <inttypes.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/climits b/libcxx/include/climits
--- a/libcxx/include/climits
+++ b/libcxx/include/climits
@@ -39,8 +39,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <limits.h>
 
+#ifndef _LIBCPP_LIMITS_H
+#   error "<climits> tried including <limits.h> but didn't find libc++'s <limits.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/clocale b/libcxx/include/clocale
--- a/libcxx/include/clocale
+++ b/libcxx/include/clocale
@@ -36,8 +36,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <locale.h>
 
+#ifndef _LIBCPP_LOCALE_H
+#   error "<clocale> tried including <locale.h> but didn't find libc++'s <locale.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cmath b/libcxx/include/cmath
--- a/libcxx/include/cmath
+++ b/libcxx/include/cmath
@@ -306,10 +306,18 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
-#include <math.h>
 #include <type_traits>
 #include <version>
 
+#include <math.h>
+
+#ifndef _LIBCPP_MATH_H
+#   error "<cmath> tried including <math.h> but didn't find libc++'s <math.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/csetjmp b/libcxx/include/csetjmp
--- a/libcxx/include/csetjmp
+++ b/libcxx/include/csetjmp
@@ -32,8 +32,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <setjmp.h>
 
+#ifndef _LIBCPP_SETJMP_H
+#   error "<csetjmp> tried including <setjmp.h> but didn't find libc++'s <setjmp.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cstddef b/libcxx/include/cstddef
--- a/libcxx/include/cstddef
+++ b/libcxx/include/cstddef
@@ -38,9 +38,17 @@
 #include <__type_traits/enable_if.h>
 #include <__type_traits/integral_constant.h>
 #include <__type_traits/is_integral.h>
-#include <stddef.h>
 #include <version>
 
+#include <stddef.h>
+
+#ifndef _LIBCPP_STDDEF_H
+#   error "<cstddef> tried including <stddef.h> but didn't find libc++'s <stddef.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cstdint b/libcxx/include/cstdint
--- a/libcxx/include/cstdint
+++ b/libcxx/include/cstdint
@@ -142,8 +142,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <stdint.h>
 
+#ifndef _LIBCPP_STDINT_H
+#   error "<cstdint> tried including <stdint.h> but didn't find libc++'s <stdint.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cstdio b/libcxx/include/cstdio
--- a/libcxx/include/cstdio
+++ b/libcxx/include/cstdio
@@ -97,8 +97,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <stdio.h>
 
+#ifndef _LIBCPP_STDIO_H
+#   error "<cstdio> tried including <stdio.h> but didn't find libc++'s <stdio.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cstdlib b/libcxx/include/cstdlib
--- a/libcxx/include/cstdlib
+++ b/libcxx/include/cstdlib
@@ -83,8 +83,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <stdlib.h>
 
+#ifndef _LIBCPP_STDLIB_H
+#   error "<cstdlib> tried including <stdlib.h> but didn't find libc++'s <stdlib.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cstring b/libcxx/include/cstring
--- a/libcxx/include/cstring
+++ b/libcxx/include/cstring
@@ -58,8 +58,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <string.h>
 
+#ifndef _LIBCPP_STRING_H
+#   error "<cstring> tried including <string.h> but didn't find libc++'s <string.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cuchar b/libcxx/include/cuchar
--- a/libcxx/include/cuchar
+++ b/libcxx/include/cuchar
@@ -36,8 +36,16 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
 #include <uchar.h>
 
+#ifndef _LIBCPP_UCHAR_H
+#   error "<cuchar> tried including <uchar.h> but didn't find libc++'s <uchar.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cwchar b/libcxx/include/cwchar
--- a/libcxx/include/cwchar
+++ b/libcxx/include/cwchar
@@ -105,8 +105,16 @@
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
 #include <cwctype>
+
 #include <wchar.h>
 
+#ifndef _LIBCPP_WCHAR_H
+#   error "<cwchar> tried including <wchar.h> but didn't find libc++'s <wchar.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/cwctype b/libcxx/include/cwctype
--- a/libcxx/include/cwctype
+++ b/libcxx/include/cwctype
@@ -52,8 +52,16 @@
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
 #include <cctype>
+
 #include <wctype.h>
 
+#ifndef _LIBCPP_WCTYPE_H
+#   error "<cwctype> tried including <wctype.h> but didn't find libc++'s <wctype.h> header. " \
+          "This usually means that your header search paths are not configured properly. " \
+          "The header search paths should contain the C++ Standard Library headers before " \
+          "any C Standard Library."
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif