diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index 213dbfc..75b7939 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -79,6 +79,7 @@
 PyBytes_FromStringAndSize(const char *bytes, Py_ssize_t size)
 {
     PyBytesObject *new;
+    int alloc;
 
     assert(size >= 0);
 
@@ -86,18 +87,23 @@
     if (new == NULL)
         return NULL;
 
-    if (size == 0)
+    if (size == 0) {
         new->ob_bytes = NULL;
+        alloc = 0;
+    }
     else {
-        new->ob_bytes = PyMem_Malloc(size);
+        alloc = size + 1;
+        new->ob_bytes = PyMem_Malloc(alloc);
         if (new->ob_bytes == NULL) {
             Py_DECREF(new);
             return NULL;
         }
         if (bytes != NULL)
             memcpy(new->ob_bytes, bytes, size);
+        new->ob_bytes[size] = '\0';  /* Trailing null byte */
     }
-    new->ob_size = new->ob_alloc = size;
+    new->ob_size = size;
+    new->ob_alloc = alloc;
 
     return (PyObject *)new;
 }
@@ -134,7 +140,7 @@
         /* Major downsize; resize down to exact size */
         alloc = size;
     }
-    else if (size <= alloc) {
+    else if (size < alloc) {
         /* Within allocated size; quick exit */
         ((PyBytesObject *)self)->ob_size = size;
         return 0;
@@ -147,6 +153,8 @@
         /* Major upsize; resize up to exact size */
         alloc = size;
     }
+    if (alloc <= size)
+        alloc = size + 1;
 
     sval = PyMem_Realloc(((PyBytesObject *)self)->ob_bytes, alloc);
     if (sval == NULL) {
@@ -158,6 +166,8 @@
     ((PyBytesObject *)self)->ob_size = size;
     ((PyBytesObject *)self)->ob_alloc = alloc;
 
+    ((PyBytesObject *)self)->ob_bytes[size] = '\0'; /* Trailing null byte */
+
     return 0;
 }
 
@@ -221,7 +231,7 @@
     size = mysize + osize;
     if (size < 0)
         return PyErr_NoMemory();
-    if (size <= self->ob_alloc)
+    if (size < self->ob_alloc)
         self->ob_size = size;
     else if (PyBytes_Resize((PyObject *)self, size) < 0)
         return NULL;
@@ -243,7 +253,7 @@
     size = mysize * count;
     if (count != 0 && size / count != mysize)
         return PyErr_NoMemory();
-    result = (PyBytesObject *)PyBytes_FromStringAndSize(NULL,  size);
+    result = (PyBytesObject *)PyBytes_FromStringAndSize(NULL, size);
     if (result != NULL && size != 0) {
         if (mysize == 1)
             memset(result->ob_bytes, self->ob_bytes[0], size);
@@ -268,7 +278,7 @@
     size = mysize * count;
     if (count != 0 && size / count != mysize)
         return PyErr_NoMemory();
-    if (size <= self->ob_alloc)
+    if (size < self->ob_alloc)
         self->ob_size = size;
     else if (PyBytes_Resize((PyObject *)self, size) < 0)
         return NULL;
@@ -703,7 +713,7 @@
         }
         bytes = PyString_AS_STRING(encoded);
         size = PyString_GET_SIZE(encoded);
-        if (size <= self->ob_alloc)
+        if (size < self->ob_alloc)
             self->ob_size = size;
         else if (PyBytes_Resize((PyObject *)self, size) < 0) {
             Py_DECREF(encoded);
diff --git a/Objects/moduleobject.c b/Objects/moduleobject.c
index 18914d8..82eabf1 100644
--- a/Objects/moduleobject.c
+++ b/Objects/moduleobject.c
@@ -72,8 +72,11 @@
 		PyErr_SetString(PyExc_SystemError, "nameless module");
 		return NULL;
 	}
-        if (PyUnicode_Check(nameobj))
-		nameobj = _PyUnicode_AsDefaultEncodedString(nameobj, "replace");
+        if (PyUnicode_Check(nameobj)) {
+		nameobj = _PyUnicode_AsDefaultEncodedString(nameobj, NULL);
+		if (nameobj == NULL)
+			return NULL;
+	}
 	return PyString_AsString(nameobj);
 }
 
diff --git a/Objects/object.c b/Objects/object.c
index ada1d1e..81f5669 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -422,7 +422,8 @@
 		return NULL;
 	if (PyUnicode_Check(res)) {
 		PyObject* str;
-		str = PyUnicode_AsEncodedString(res, NULL, NULL);
+		str = _PyUnicode_AsDefaultEncodedString(res, NULL);
+		Py_XINCREF(str);
 		Py_DECREF(res);
 		if (str)
 			res = str;
@@ -929,12 +930,12 @@
 	PyTypeObject *tp = v->ob_type;
 	int err;
 
-	if (!PyString_Check(name)){
+	if (!PyString_Check(name)) {
 		/* The Unicode to string conversion is done here because the
 		   existing tp_setattro slots expect a string object as name
 		   and we wouldn't want to break those. */
 		if (PyUnicode_Check(name)) {
-			name = PyUnicode_AsEncodedString(name, NULL, NULL);
+			name = _PyUnicode_AsDefaultEncodedString(name, NULL);
 			if (name == NULL)
 				return -1;
 		}
@@ -946,8 +947,7 @@
 			return -1;
 		}
 	}
-	else
-		Py_INCREF(name);
+	Py_INCREF(name);
 
 	PyString_InternInPlace(&name);
 	if (tp->tp_setattro != NULL) {
@@ -961,6 +961,7 @@
 		return err;
 	}
 	Py_DECREF(name);
+	assert(name->ob_refcnt >= 1);
 	if (tp->tp_getattr == NULL && tp->tp_getattro == NULL)
 		PyErr_Format(PyExc_TypeError,
 			     "'%.100s' object has no attributes "
diff --git a/Objects/stringobject.c b/Objects/stringobject.c
index f74c5dc..2ebaca8 100644
--- a/Objects/stringobject.c
+++ b/Objects/stringobject.c
@@ -3181,9 +3181,9 @@
     v = PyString_AsEncodedObject((PyObject *)self, encoding, errors);
     if (v == NULL)
         goto onError;
-    if (!PyString_Check(v) && !PyUnicode_Check(v)) {
+    if (!PyBytes_Check(v)) {
         PyErr_Format(PyExc_TypeError,
-                     "encoder did not return a string/unicode object "
+                     "[str8] encoder did not return a bytes object "
                      "(type=%.400s)",
                      v->ob_type->tp_name);
         Py_DECREF(v);
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index d4a7e7e..db3f9c4 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -104,13 +104,9 @@
 static PyUnicodeObject *unicode_latin1[256];
 
 /* Default encoding to use and assume when NULL is passed as encoding
-   parameter; it is initialized by _PyUnicode_Init().
-
-   Always use the PyUnicode_SetDefaultEncoding() and
-   PyUnicode_GetDefaultEncoding() APIs to access this global.
-
-*/
-static char unicode_default_encoding[100];
+   parameter; it is fixed to "utf-8".  Always use the
+   PyUnicode_GetDefaultEncoding() API to access this global. */
+static const char unicode_default_encoding[] = "utf-8";
 
 Py_UNICODE
 PyUnicode_GetMax(void)
@@ -711,10 +707,19 @@
     v = PyCodec_Encode(unicode, encoding, errors);
     if (v == NULL)
         goto onError;
-    if (!PyString_Check(v)) {
+    if (!PyBytes_Check(v)) {
+        if (PyString_Check(v)) {
+            /* Old codec, turn it into bytes */
+            PyObject *b = PyBytes_FromObject(v);
+            Py_DECREF(v);
+            return b;
+        }
         PyErr_Format(PyExc_TypeError,
-                     "encoder did not return a string object (type=%.400s)",
-                     v->ob_type->tp_name);
+                     "encoder did not return a bytes object "
+                     "(type=%.400s, encoding=%.20s, errors=%.20s)",
+                     v->ob_type->tp_name,
+                     encoding ? encoding : "NULL",
+                     errors ? errors : "NULL");
         Py_DECREF(v);
         goto onError;
     }
@@ -728,12 +733,28 @@
 					    const char *errors)
 {
     PyObject *v = ((PyUnicodeObject *)unicode)->defenc;
-
+    PyObject *b;
     if (v)
         return v;
-    v = PyUnicode_AsEncodedString(unicode, NULL, errors);
-    if (v && errors == NULL)
+    if (errors != NULL)
+        Py_FatalError("non-NULL encoding in _PyUnicode_AsDefaultEncodedString");
+    if (errors == NULL) {
+        b = PyUnicode_EncodeUTF8(PyUnicode_AS_UNICODE(unicode),
+                                 PyUnicode_GET_SIZE(unicode),
+                                 NULL);
+    }
+    else {
+        b = PyUnicode_AsEncodedString(unicode, NULL, errors);
+    }
+    if (!b)
+        return NULL;
+    v = PyString_FromStringAndSize(PyBytes_AsString(b),
+                                   PyBytes_Size(b));
+    Py_DECREF(b);
+    if (!errors) {
+        Py_XINCREF(v);
         ((PyUnicodeObject *)unicode)->defenc = v;
+    }
     return v;
 }
 
@@ -768,21 +789,13 @@
 
 int PyUnicode_SetDefaultEncoding(const char *encoding)
 {
-    PyObject *v;
-
-    /* Make sure the encoding is valid. As side effect, this also
-       loads the encoding into the codec registry cache. */
-    v = _PyCodec_Lookup(encoding);
-    if (v == NULL)
-	goto onError;
-    Py_DECREF(v);
-    strncpy(unicode_default_encoding,
-	    encoding,
-	    sizeof(unicode_default_encoding));
+    if (strcmp(encoding, unicode_default_encoding) != 0) {
+        PyErr_Format(PyExc_ValueError,
+                     "Can only set default encoding to %s",
+                     unicode_default_encoding);
+        return -1;
+    }
     return 0;
-
- onError:
-    return -1;
 }
 
 /* error handling callback helper:
@@ -1429,10 +1442,10 @@
         nallocated = size * 4;
         if (nallocated / 4 != size)  /* overflow! */
             return PyErr_NoMemory();
-        v = PyString_FromStringAndSize(NULL, nallocated);
+        v = PyBytes_FromStringAndSize(NULL, nallocated);
         if (v == NULL)
             return NULL;
-        p = PyString_AS_STRING(v);
+        p = PyBytes_AS_STRING(v);
     }
 
     for (i = 0; i < size;) {
@@ -1480,13 +1493,13 @@
         /* This was stack allocated. */
         nneeded = p - stackbuf;
         assert(nneeded <= nallocated);
-        v = PyString_FromStringAndSize(stackbuf, nneeded);
+        v = PyBytes_FromStringAndSize(stackbuf, nneeded);
     }
     else {
     	/* Cut back to size actually needed. */
-        nneeded = p - PyString_AS_STRING(v);
+        nneeded = p - PyBytes_AS_STRING(v);
         assert(nneeded <= nallocated);
-        _PyString_Resize(&v, nneeded);
+        PyBytes_Resize(v, nneeded);
     }
     return v;
 
@@ -2588,12 +2601,12 @@
 
     /* allocate enough for a simple encoding without
        replacements, if we need more, we'll resize */
-    res = PyString_FromStringAndSize(NULL, size);
+    res = PyBytes_FromStringAndSize(NULL, size);
     if (res == NULL)
         goto onError;
     if (size == 0)
 	return res;
-    str = PyString_AS_STRING(res);
+    str = PyBytes_AS_STRING(res);
     ressize = size;
 
     while (p<endp) {
@@ -2643,7 +2656,7 @@
 		    p = collend;
 		    break;
 		case 4: /* xmlcharrefreplace */
-		    respos = str-PyString_AS_STRING(res);
+		    respos = str - PyBytes_AS_STRING(res);
 		    /* determine replacement size (temporarily (mis)uses p) */
 		    for (p = collstart, repsize = 0; p < collend; ++p) {
 			if (*p<10)
@@ -2670,9 +2683,9 @@
 		    if (requiredsize > ressize) {
 			if (requiredsize<2*ressize)
 			    requiredsize = 2*ressize;
-			if (_PyString_Resize(&res, requiredsize))
+			if (PyBytes_Resize(res, requiredsize))
 			    goto onError;
-			str = PyString_AS_STRING(res) + respos;
+			str = PyBytes_AS_STRING(res) + respos;
 			ressize = requiredsize;
 		    }
 		    /* generate replacement (temporarily (mis)uses p) */
@@ -2690,17 +2703,17 @@
 		    /* need more space? (at least enough for what we
 		       have+the replacement+the rest of the string, so
 		       we won't have to check space for encodable characters) */
-		    respos = str-PyString_AS_STRING(res);
+		    respos = str - PyBytes_AS_STRING(res);
 		    repsize = PyUnicode_GET_SIZE(repunicode);
 		    requiredsize = respos+repsize+(endp-collend);
 		    if (requiredsize > ressize) {
 			if (requiredsize<2*ressize)
 			    requiredsize = 2*ressize;
-			if (_PyString_Resize(&res, requiredsize)) {
+			if (PyBytes_Resize(res, requiredsize)) {
 			    Py_DECREF(repunicode);
 			    goto onError;
 			}
-			str = PyString_AS_STRING(res) + respos;
+			str = PyBytes_AS_STRING(res) + respos;
 			ressize = requiredsize;
 		    }
 		    /* check if there is anything unencodable in the replacement
@@ -2721,10 +2734,10 @@
 	}
     }
     /* Resize if we allocated to much */
-    respos = str-PyString_AS_STRING(res);
+    respos = str - PyBytes_AS_STRING(res);
     if (respos<ressize)
        /* If this falls res will be NULL */
-	_PyString_Resize(&res, respos);
+	PyBytes_Resize(res, respos);
     Py_XDECREF(errorHandler);
     Py_XDECREF(exc);
     return res;
@@ -2979,20 +2992,20 @@
 
     if (*repr == NULL) {
 	/* Create string object */
-	*repr = PyString_FromStringAndSize(NULL, mbcssize);
+	*repr = PyBytes_FromStringAndSize(NULL, mbcssize);
 	if (*repr == NULL)
 	    return -1;
     }
     else {
 	/* Extend string object */
-	n = PyString_Size(*repr);
-	if (_PyString_Resize(repr, n + mbcssize) < 0)
+	n = PyBytes_Size(*repr);
+	if (PyBytes_Resize(*repr, n + mbcssize) < 0)
 	    return -1;
     }
 
     /* Do the conversion */
     if (size > 0) {
-	char *s = PyString_AS_STRING(*repr) + n;
+	char *s = PyBytes_AS_STRING(*repr) + n;
 	if (0 == WideCharToMultiByte(CP_ACP, 0, p, size, s, mbcssize, NULL, NULL)) {
 	    PyErr_SetFromWindowsErrWithFilename(0, NULL);
 	    return -1;
@@ -5630,9 +5643,9 @@
     v = PyUnicode_AsEncodedObject((PyObject *)self, encoding, errors);
     if (v == NULL)
         goto onError;
-    if (!PyString_Check(v) && !PyUnicode_Check(v)) {
+    if (!PyBytes_Check(v)) {
         PyErr_Format(PyExc_TypeError,
-                     "encoder did not return a string/unicode object "
+                     "encoder did not return a bytes object "
                      "(type=%.400s)",
                      v->ob_type->tp_name);
         Py_DECREF(v);
@@ -6797,9 +6810,11 @@
 }
 
 static
-PyObject *unicode_str(PyUnicodeObject *self)
+PyObject *unicode_str(PyObject *self)
 {
-    return PyUnicode_AsEncodedString((PyObject *)self, NULL, NULL);
+    PyObject *res = _PyUnicode_AsDefaultEncodedString(self, NULL);
+    Py_XINCREF(res);
+    return res;
 }
 
 PyDoc_STRVAR(swapcase__doc__,
@@ -8021,7 +8036,6 @@
     if (!unicode_empty)
 	return;
 
-    strcpy(unicode_default_encoding, "ascii");
     for (i = 0; i < 256; i++)
 	unicode_latin1[i] = NULL;
     if (PyType_Ready(&PyUnicode_Type) < 0)