diff --git a/libcxx/include/barrier b/libcxx/include/barrier
--- a/libcxx/include/barrier
+++ b/libcxx/include/barrier
@@ -59,7 +59,7 @@
 #endif
 
 #ifdef _LIBCPP_HAS_NO_THREADS
-# error <barrier> is not supported on this single threaded system
+# error "<barrier> is not supported since libc++ has been configured without support for threads."
 #endif
 
 _LIBCPP_PUSH_MACROS
diff --git a/libcxx/include/filesystem b/libcxx/include/filesystem
--- a/libcxx/include/filesystem
+++ b/libcxx/include/filesystem
@@ -261,7 +261,7 @@
 #include <version>
 
 #if defined(_LIBCPP_HAS_NO_FILESYSTEM_LIBRARY)
-# error "The Filesystem library is not supported since libc++ has been configured with LIBCXX_ENABLE_FILESYSTEM disabled"
+# error "The <filesystem> library is not supported since libc++ has been configured without support for a filesystem."
 #endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
diff --git a/libcxx/include/future b/libcxx/include/future
--- a/libcxx/include/future
+++ b/libcxx/include/future
@@ -383,8 +383,8 @@
 #endif
 
 #ifdef _LIBCPP_HAS_NO_THREADS
-#error <future> is not supported on this single threaded system
-#else // !_LIBCPP_HAS_NO_THREADS
+# error "<future> is not supported since libc++ has been configured without support for threads."
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -2432,6 +2432,4 @@
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // !_LIBCPP_HAS_NO_THREADS
-
 #endif // _LIBCPP_FUTURE
diff --git a/libcxx/include/ios b/libcxx/include/ios
--- a/libcxx/include/ios
+++ b/libcxx/include/ios
@@ -210,8 +210,13 @@
 
 */
 
-#include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+
+#if defined(_LIBCPP_HAS_NO_LOCALIZATION)
+#   error "The iostreams library is not supported since libc++ has been configured without support for localization."
+#endif
+
+#include <__assert> // all public C++ headers provide the assertion handler
 #include <__ios/fpos.h>
 #include <__locale>
 #include <__utility/swap.h>
diff --git a/libcxx/include/latch b/libcxx/include/latch
--- a/libcxx/include/latch
+++ b/libcxx/include/latch
@@ -51,7 +51,7 @@
 #endif
 
 #ifdef _LIBCPP_HAS_NO_THREADS
-# error <latch> is not supported on this single threaded system
+# error "<latch> is not supported since libc++ has been configured without support for threads."
 #endif
 
 _LIBCPP_PUSH_MACROS
diff --git a/libcxx/include/locale.h b/libcxx/include/locale.h
--- a/libcxx/include/locale.h
+++ b/libcxx/include/locale.h
@@ -36,7 +36,7 @@
 #include <__config>
 
 #if defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#   error "The Localization library is not supported since libc++ has been configured with LIBCXX_ENABLE_LOCALIZATION disabled"
+#   error "<locale.h> is not supported since libc++ has been configured without support for localization."
 #endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
diff --git a/libcxx/include/semaphore b/libcxx/include/semaphore
--- a/libcxx/include/semaphore
+++ b/libcxx/include/semaphore
@@ -59,7 +59,7 @@
 #endif
 
 #ifdef _LIBCPP_HAS_NO_THREADS
-# error <semaphore> is not supported on this single threaded system
+# error "<semaphore> is not supported since libc++ has been configured without support for threads."
 #endif
 
 _LIBCPP_PUSH_MACROS
diff --git a/libcxx/include/shared_mutex b/libcxx/include/shared_mutex
--- a/libcxx/include/shared_mutex
+++ b/libcxx/include/shared_mutex
@@ -140,8 +140,8 @@
 #endif
 
 #ifdef _LIBCPP_HAS_NO_THREADS
-#error <shared_mutex> is not supported on this single threaded system
-#else // !_LIBCPP_HAS_NO_THREADS
+# error "<shared_mutex> is not supported since libc++ has been configured without support for threads."
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -501,8 +501,6 @@
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // !_LIBCPP_HAS_NO_THREADS
-
 #endif // _LIBCPP_STD_VER > 11
 
 _LIBCPP_POP_MACROS
diff --git a/libcxx/include/thread b/libcxx/include/thread
--- a/libcxx/include/thread
+++ b/libcxx/include/thread
@@ -105,8 +105,8 @@
 #include <__undef_macros>
 
 #ifdef _LIBCPP_HAS_NO_THREADS
-#error <thread> is not supported on this single threaded system
-#else // !_LIBCPP_HAS_NO_THREADS
+# error "<thread> is not supported since libc++ has been configured without support for threads."
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -401,8 +401,6 @@
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // !_LIBCPP_HAS_NO_THREADS
-
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP_THREAD