diff -r c6892ce7e56f Modules/_localemodule.c
--- a/Modules/_localemodule.c	Mon Sep 17 09:01:03 2012 +0200
+++ b/Modules/_localemodule.c	Mon Sep 17 14:32:33 2012 +0300
@@ -254,7 +254,12 @@
         PyErr_NoMemory();
         goto exit;
     }
+    errno = 0;
     n2 = wcsxfrm(buf, s, n1);
+    if (errno) {
+        PyErr_SetFromErrno(PyExc_OSError);
+        goto exit;
+    }
     if (n2 >= (size_t)n1) {
         /* more space needed */
         wchar_t * new_buf = PyMem_Realloc(buf, (n2+1)*sizeof(wchar_t));
@@ -263,7 +268,12 @@
             goto exit;
         }
         buf = new_buf;
+        errno = 0;
         n2 = wcsxfrm(buf, s, n2+1);
+        if (errno) {
+            PyErr_SetFromErrno(PyExc_OSError);
+            goto exit;
+        }
     }
     result = PyUnicode_FromWideChar(buf, n2);
 exit: