diff -r 1f767f834e67 Lib/test/test_peepholer.py
--- a/Lib/test/test_peepholer.py	Thu Apr 14 07:51:57 2011 +0300
+++ b/Lib/test/test_peepholer.py	Thu Apr 14 15:51:14 2011 +0300
@@ -205,6 +205,24 @@
         asm = dis_single('a="x"*1000')
         self.assertIn('(1000)', asm)
 
+    def test_binary_subscr_on_unicode(self):
+        # valid code get optimized
+        asm = dis_single('"foo"[0]')
+        self.assertIn("('f')", asm)
+        self.assertNotIn('BINARY_SUBSCR', asm)
+        asm = dis_single('"\u0061\uffff"[1]')
+        self.assertIn("('\\uffff')", asm)
+        self.assertNotIn('BINARY_SUBSCR', asm)
+
+        # invalid code doesn't get optimized
+        # out of range
+        asm = dis_single('"fuu"[10]')
+        self.assertIn('BINARY_SUBSCR', asm)
+        # non-BMP char (see #5057)
+        asm = dis_single('"\U00012345"[0]')
+        self.assertIn('BINARY_SUBSCR', asm)
+
+
     def test_folding_of_unaryops_on_constants(self):
         for line, elem in (
             ('-0.5', '(-0.5)'),                     # unary negative
diff -r 1f767f834e67 Python/peephole.c
--- a/Python/peephole.c	Thu Apr 14 07:51:57 2011 +0300
+++ b/Python/peephole.c	Thu Apr 14 15:51:14 2011 +0300
@@ -183,6 +183,23 @@
             break;
         case BINARY_SUBSCR:
             newconst = PyObject_GetItem(v, w);
+            /* #5057: if v is unicode, there might be differences between
+               wide and narrow builds in cases like '\U00012345'[0].
+               Wide builds will return a non-BMP char, whereas narrow builds
+               will return a surrogate.  In both the cases skip the
+               optimization in order to produce compatible pycs.
+             */
+            if (newconst != NULL &&
+                PyUnicode_Check(v) && PyUnicode_Check(newconst)) {
+                Py_UNICODE ch = PyUnicode_AS_UNICODE(newconst)[0];
+#ifdef Py_UNICODE_WIDE
+                if (ch > 0xFFFF)
+                    return 0;
+#else
+                if (ch >= 0xD800 && ch <= 0xDFFF)
+                    return 0;
+#endif
+            }
             break;
         case BINARY_LSHIFT:
             newconst = PyNumber_Lshift(v, w);