diff --git a/Lib/test/test_pep263.py b/Lib/test/test_pep263.py
index 05ca47f..587b2fc 100644
--- a/Lib/test/test_pep263.py
+++ b/Lib/test/test_pep263.py
@@ -36,6 +36,14 @@
         exec(c, d)
         self.assertEquals(d['\xc6'], '\xc6')
 
+    def test_issue3297(self):
+        c = compile("a, b = '\U0001010F', '\\U0001010F'", "dummy", "exec")
+        d = {}
+        exec(c, d)
+        self.assertEqual(d['a'], d['b'])
+        self.assertEqual(len(d['a']), len(d['b']))
+        self.assertEqual(ascii(d['a']), ascii(d['b']))
+
 def test_main():
     support.run_unittest(PEP263Test)
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 96320f7..030430a 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
 Core and Builtins
 -----------------
 
+- Issue #3297: On wide unicode builds, do not split unicode characters into
+  surrogates.
+
 - Remove length limitation when constructing a complex number from a string.
 
 - Issue #1087418: Boost performance of bitwise operations for longs.
diff --git a/Python/ast.c b/Python/ast.c
index c3edea3..c6a6417 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -3246,10 +3246,11 @@
         u = NULL;
     } else {
         /* check for integer overflow */
-        if (len > PY_SIZE_MAX / 4)
+        if (len > PY_SIZE_MAX / 6)
             return NULL;
-        /* "\XX" may become "\u005c\uHHLL" (12 bytes) */
-        u = PyBytes_FromStringAndSize((char *)NULL, len * 4);
+        /* "ä" (2 bytes) may become "\U000000E4" (10 bytes), or 1:5
+           "\ä" (3 bytes) may become "\u005c\U000000E4" (16 bytes), or ~1:6 */
+        u = PyBytes_FromStringAndSize((char *)NULL, len * 6);
         if (u == NULL)
             return NULL;
         p = buf = PyBytes_AsString(u);
@@ -3266,20 +3267,24 @@
                 PyObject *w;
                 char *r;
                 Py_ssize_t rn, i;
-                w = decode_utf8(c, &s, end, "utf-16-be");
+                w = decode_utf8(c, &s, end, "utf-32-be");
                 if (w == NULL) {
                     Py_DECREF(u);
                     return NULL;
                 }
                 r = PyBytes_AS_STRING(w);
                 rn = Py_SIZE(w);
-                assert(rn % 2 == 0);
-                for (i = 0; i < rn; i += 2) {
-                    sprintf(p, "\\u%02x%02x",
+                assert(rn % 4 == 0);
+                for (i = 0; i < rn; i += 4) {
+                    sprintf(p, "\\U%02x%02x%02x%02x",
                             r[i + 0] & 0xFF,
-                            r[i + 1] & 0xFF);
-                    p += 6;
+                            r[i + 1] & 0xFF,
+                            r[i + 2] & 0xFF,
+                            r[i + 3] & 0xFF);
+                    p += 10;
                 }
+                /* Should be impossible to overflow */
+                assert(p - buf <= Py_SIZE(u));
                 Py_DECREF(w);
             } else {
                 *p++ = *s++;