Index: include/__config
===================================================================
--- include/__config
+++ include/__config
@@ -635,6 +635,17 @@
 #define _LIBCPP_WCTYPE_IS_MASK
 #endif
 
+#if defined(ELAST)
+#define _LIBCPP_ELAST ELAST
+#elif defined(__linux__)
+#define _LIBCPP_ELAST 4095
+#elif defined(_NEWLIB_VERSION)
+#define _LIBCPP_ELAST __ELASTERROR
+#else
+// Warn here so that the person doing the libcxx port has an easier time:
+#warning This platform's ELAST hasn't been ported yet
+#endif
+
 #ifndef _LIBCPP_TRIVIAL_PAIR_COPY_CTOR
 #  define _LIBCPP_TRIVIAL_PAIR_COPY_CTOR 1
 #endif
Index: src/ios.cpp
===================================================================
--- src/ios.cpp
+++ src/ios.cpp
@@ -7,6 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "__config"
 #include "ios"
 #include "streambuf"
 #include "istream"
@@ -52,11 +53,9 @@
 __iostream_category::message(int ev) const
 {
     if (ev != static_cast<int>(io_errc::stream)
-#ifdef ELAST
-        && ev <= ELAST
-#elif defined(__linux__)
-        && ev <= 4095
-#endif  // ELAST
+#ifdef _LIBCPP_ELAST
+        && ev <= _LIBCPP_ELAST
+#endif  // _LIBCPP_ELAST
         )
         return __do_message::message(ev);
     return string("unspecified iostream_category error");
Index: src/system_error.cpp
===================================================================
--- src/system_error.cpp
+++ src/system_error.cpp
@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #define _LIBCPP_BUILDING_SYSTEM_ERROR
+#include "__config"
 #include "system_error"
 #include "string"
 #include "cstring"
@@ -65,13 +66,10 @@
 string
 __generic_error_category::message(int ev) const
 {
-#ifdef ELAST
-    if (ev > ELAST)
+#ifdef _LIBCPP_ELAST
+    if (ev > _LIBCPP_ELAST)
       return string("unspecified generic_category error");
-#elif defined(__linux__)
-    if (ev > 4095)
-      return string("unspecified generic_category error");
-#endif  // ELAST
+#endif  // _LIBCPP_ELAST
     return __do_message::message(ev);
 }
 
@@ -100,26 +98,20 @@
 string
 __system_error_category::message(int ev) const
 {
-#ifdef ELAST
-    if (ev > ELAST)
-      return string("unspecified system_category error");
-#elif defined(__linux__)
-    if (ev > 4095)
+#ifdef _LIBCPP_ELAST
+    if (ev > _LIBCPP_ELAST)
       return string("unspecified system_category error");
-#endif  // ELAST
+#endif  // _LIBCPP_ELAST
     return __do_message::message(ev);
 }
 
 error_condition
 __system_error_category::default_error_condition(int ev) const _NOEXCEPT
 {
-#ifdef ELAST
-    if (ev > ELAST)
-      return error_condition(ev, system_category());
-#elif defined(__linux__)
-    if (ev > 4095)
+#ifdef _LIBCPP_ELAST
+    if (ev > _LIBCPP_ELAST)
       return error_condition(ev, system_category());
-#endif  // ELAST
+#endif  // _LIBCPP_ELAST
     return error_condition(ev, generic_category());
 }