diff -r d1c11a78b43a Lib/test/test_sys.py
--- a/Lib/test/test_sys.py	Tue Nov 10 19:52:20 2015 +0200
+++ b/Lib/test/test_sys.py	Tue Nov 10 22:42:22 2015 +0200
@@ -691,7 +691,7 @@ class SysModuleTest(unittest.TestCase):
         args = [sys.executable, "-c", code]
         if isolated:
             args.append("-I")
-        elif encoding:
+        elif encoding is not None:
             env['PYTHONIOENCODING'] = encoding
         p = subprocess.Popen(args,
                               stdout=subprocess.PIPE,
@@ -709,14 +709,31 @@ class SysModuleTest(unittest.TestCase):
                          'stderr: backslashreplace\n')
 
         # replace the default error handler
-        out = self.c_locale_get_error_handler(encoding=':strict')
+        out = self.c_locale_get_error_handler(encoding=':ignore')
+        self.assertEqual(out,
+                         'stdin: ignore\n'
+                         'stdout: ignore\n'
+                         'stderr: backslashreplace\n')
+
+        # force the encoding
+        out = self.c_locale_get_error_handler(encoding='iso8859-1')
+        self.assertEqual(out,
+                         'stdin: strict\n'
+                         'stdout: strict\n'
+                         'stderr: backslashreplace\n')
+        out = self.c_locale_get_error_handler(encoding='iso8859-1:')
         self.assertEqual(out,
                          'stdin: strict\n'
                          'stdout: strict\n'
                          'stderr: backslashreplace\n')
 
-        # force the encoding
-        out = self.c_locale_get_error_handler(encoding='iso8859-1')
+        # have no any effect
+        out = self.c_locale_get_error_handler(encoding=':')
+        self.assertEqual(out,
+                         'stdin: surrogateescape\n'
+                         'stdout: surrogateescape\n'
+                         'stderr: backslashreplace\n')
+        out = self.c_locale_get_error_handler(encoding='')
         self.assertEqual(out,
                          'stdin: surrogateescape\n'
                          'stdout: surrogateescape\n'
diff -r d1c11a78b43a Python/pylifecycle.c
--- a/Python/pylifecycle.c	Tue Nov 10 19:52:20 2015 +0200
+++ b/Python/pylifecycle.c	Tue Nov 10 22:42:22 2015 +0200
@@ -1138,15 +1138,6 @@ initstdio(void)
     encoding = _Py_StandardStreamEncoding;
     errors = _Py_StandardStreamErrors;
     if (!encoding || !errors) {
-        if (!errors) {
-            /* When the LC_CTYPE locale is the POSIX locale ("C locale"),
-               stdin and stdout use the surrogateescape error handler by
-               default, instead of the strict error handler. */
-            char *loc = setlocale(LC_CTYPE, NULL);
-            if (loc != NULL && strcmp(loc, "C") == 0)
-                errors = "surrogateescape";
-        }
-
         pythonioencoding = Py_GETENV("PYTHONIOENCODING");
         if (pythonioencoding) {
             char *err;
@@ -1159,7 +1150,7 @@ initstdio(void)
             if (err) {
                 *err = '\0';
                 err++;
-                if (*err && !_Py_StandardStreamErrors) {
+                if (*err && !errors) {
                     errors = err;
                 }
             }
@@ -1167,6 +1158,14 @@ initstdio(void)
                 encoding = pythonioencoding;
             }
         }
+        if (!errors && !(pythonioencoding && *pythonioencoding)) {
+            /* When the LC_CTYPE locale is the POSIX locale ("C locale"),
+               stdin and stdout use the surrogateescape error handler by
+               default, instead of the strict error handler. */
+            char *loc = setlocale(LC_CTYPE, NULL);
+            if (loc != NULL && strcmp(loc, "C") == 0)
+                errors = "surrogateescape";
+        }
     }
 
     /* Set sys.stdin */