diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
index e6b3cb0..604fdf2 100644
--- a/Lib/test/test_unicode.py
+++ b/Lib/test/test_unicode.py
@@ -847,6 +847,9 @@
 
         self.assertEqual(str(b'+3ADYAA-', 'utf-7', 'replace'), '\ufffd')
 
+        # Issue #2242: crash on some Windows/MSVC versions
+        self.assertRaises(UnicodeDecodeError, b'+\xc1'.decode, 'utf-7')
+
     def test_codecs_utf8(self):
         self.assertEqual(''.encode('utf-8'), b'')
         self.assertEqual('\u20ac'.encode('utf-8'), b'\xe2\x82\xac')
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index b0b525a..838f537 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -1727,7 +1727,7 @@
     while (s < e) {
         Py_UNICODE ch;
         restart:
-        ch = *s;
+        ch = (unsigned char) *s;
 
         if (inShift) {
             if ((ch == '-') || !B64CHAR(ch)) {