Index: libcxx/trunk/include/__config
===================================================================
--- libcxx/trunk/include/__config
+++ libcxx/trunk/include/__config
@@ -904,6 +904,12 @@
 #define _LIBCPP_HAS_NO_BUILTIN_ADDRESSOF
 #endif
 
+#if !defined(_LIBCPP_HAS_NO_OFF_T_FUNCTIONS)
+#if defined(_WIN32) || defined(_NEWLIB_VERSION)
+#define _LIBCPP_HAS_NO_OFF_T_FUNCTIONS
+#endif
+#endif
+
 #endif // __cplusplus
 
 #endif // _LIBCPP_CONFIG
Index: libcxx/trunk/include/fstream
===================================================================
--- libcxx/trunk/include/fstream
+++ libcxx/trunk/include/fstream
@@ -813,7 +813,7 @@
     default:
         return pos_type(off_type(-1));
     }
-#if defined(_WIN32) || defined(_NEWLIB_VERSION)
+#if defined(_LIBCPP_HAS_NO_OFF_T_FUNCTIONS)
     if (fseek(__file_, __width > 0 ? __width * __off : 0, __whence))
         return pos_type(off_type(-1));
     pos_type __r = ftell(__file_);
@@ -832,7 +832,7 @@
 {
     if (__file_ == 0 || sync())
         return pos_type(off_type(-1));
-#if defined(_WIN32) || defined(_NEWLIB_VERSION)
+#if defined(_LIBCPP_HAS_NO_OFF_T_FUNCTIONS)
     if (fseek(__file_, __sp, SEEK_SET))
         return pos_type(off_type(-1));
 #else
@@ -896,7 +896,7 @@
                 }
             }
         }
-#if defined(_WIN32) || defined(_NEWLIB_VERSION)
+#if defined(_LIBCPP_HAS_NO_OFF_T_FUNCTIONS)
         if (fseek(__file_, -__c, SEEK_CUR))
             return -1;
 #else