diff --git a/swift/common/constraints.py b/swift/common/constraints.py
index 1d4d80cf05..47088d35ea 100644
--- a/swift/common/constraints.py
+++ b/swift/common/constraints.py
@@ -24,7 +24,7 @@ from six.moves import urllib
 from swift.common import utils, exceptions
 from swift.common.swob import HTTPBadRequest, HTTPLengthRequired, \
     HTTPRequestEntityTooLarge, HTTPPreconditionFailed, HTTPNotImplemented, \
-    HTTPException
+    HTTPException, str_from_wsgi
 
 MAX_FILE_SIZE = 5368709122
 MAX_META_NAME_LENGTH = 128
@@ -141,8 +141,8 @@ def check_metadata(req, target_type):
         if not key:
             return HTTPBadRequest(body='Metadata name cannot be empty',
                                   request=req, content_type='text/plain')
-        bad_key = not check_utf8(key)
-        bad_value = value and not check_utf8(value)
+        bad_key = not check_utf8(str_from_wsgi(key))
+        bad_value = value and not check_utf8(str_from_wsgi(value))
         if target_type in ('account', 'container') and (bad_key or bad_value):
             return HTTPBadRequest(body='Metadata must be valid UTF-8',
                                   request=req, content_type='text/plain')
@@ -215,7 +215,7 @@ def check_object_creation(req, object_name):
         return HTTPBadRequest(request=req, body=e.body,
                               content_type='text/plain')
 
-    if not check_utf8(req.headers['Content-Type']):
+    if not check_utf8(str_from_wsgi(req.headers['Content-Type'])):
         return HTTPBadRequest(request=req, body='Invalid Content-Type',
                               content_type='text/plain')
     return check_metadata(req, 'object')
@@ -359,16 +359,18 @@ def check_utf8(string):
         return False
     try:
         if isinstance(string, six.text_type):
-            string.encode('utf-8')
+            encoded = string.encode('utf-8')
+            decoded = string
         else:
+            encoded = string
             decoded = string.decode('UTF-8')
-            if decoded.encode('UTF-8') != string:
+            if decoded.encode('UTF-8') != encoded:
                 return False
-            # A UTF-8 string with surrogates in it is invalid.
-            if any(0xD800 <= ord(codepoint) <= 0xDFFF
-                   for codepoint in decoded):
-                return False
-        return '\x00' not in string
+        # A UTF-8 string with surrogates in it is invalid.
+        if any(0xD800 <= ord(codepoint) <= 0xDFFF
+               for codepoint in decoded):
+            return False
+        return b'\x00' not in encoded
     # If string is unicode, decode() will raise UnicodeEncodeError
     # So, we should catch both UnicodeDecodeError & UnicodeEncodeError
     except UnicodeError:
@@ -392,7 +394,7 @@ def check_name_format(req, name, target_type):
             body='%s name cannot be empty' % target_type)
     if isinstance(name, six.text_type):
         name = name.encode('utf-8')
-    if '/' in name:
+    if b'/' in name:
         raise HTTPPreconditionFailed(
             request=req,
             body='%s name cannot contain slashes' % target_type)
diff --git a/swift/common/swob.py b/swift/common/swob.py
index b7163065d2..2b097d1d5d 100644
--- a/swift/common/swob.py
+++ b/swift/common/swob.py
@@ -219,7 +219,11 @@ def _header_int_property(header):
 
 
 def header_to_environ_key(header_name):
-    header_name = 'HTTP_' + header_name.replace('-', '_').upper()
+    # Why the to/from wsgi dance? Headers that include something like b'\xff'
+    # on the wire get translated to u'\u00ff' on py3, which gets upper()ed to
+    # u'\u0178', which is nonsense in a WSGI string.
+    real_header = str_from_wsgi(header_name)
+    header_name = 'HTTP_' + str_to_wsgi(real_header.upper()).replace('-', '_')
     if header_name == 'HTTP_CONTENT_LENGTH':
         return 'CONTENT_LENGTH'
     if header_name == 'HTTP_CONTENT_TYPE':
@@ -251,8 +255,10 @@ class HeaderEnvironProxy(MutableMapping):
     def __setitem__(self, key, value):
         if value is None:
             self.environ.pop(header_to_environ_key(key), None)
-        elif isinstance(value, six.text_type):
+        elif six.PY2 and isinstance(value, six.text_type):
             self.environ[header_to_environ_key(key)] = value.encode('utf-8')
+        elif not six.PY2 and isinstance(value, six.binary_type):
+            self.environ[header_to_environ_key(key)] = value.decode('latin1')
         else:
             self.environ[header_to_environ_key(key)] = str(value)
 
@@ -263,7 +269,8 @@ class HeaderEnvironProxy(MutableMapping):
         del self.environ[header_to_environ_key(key)]
 
     def keys(self):
-        keys = [key[5:].replace('_', '-').title()
+        # See the to/from WSGI comment in header_to_environ_key
+        keys = [str_to_wsgi(str_from_wsgi(key[5:]).replace('_', '-').title())
                 for key in self.environ if key.startswith('HTTP_')]
         if 'CONTENT_LENGTH' in self.environ:
             keys.append('Content-Length')
@@ -272,6 +279,18 @@ class HeaderEnvironProxy(MutableMapping):
         return keys
 
 
+def str_from_wsgi(wsgi_str):
+    if six.PY2:
+        return wsgi_str
+    return wsgi_str.encode('latin1').decode('utf8', errors='surrogateescape')
+
+
+def str_to_wsgi(native_str):
+    if six.PY2:
+        return native_str
+    return native_str.encode('utf8', errors='surrogateescape').decode('latin1')
+
+
 def _resp_status_property():
     """
     Set and retrieve the value of Response.status
diff --git a/test/unit/common/test_constraints.py b/test/unit/common/test_constraints.py
index 18bbc66846..0e7bfdb754 100644
--- a/test/unit/common/test_constraints.py
+++ b/test/unit/common/test_constraints.py
@@ -44,22 +44,23 @@ class TestConstraints(unittest.TestCase):
         resp = constraints.check_metadata(Request.blank(
             '/', headers=headers), 'object')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Metadata name cannot be empty', resp.body)
+        self.assertIn(b'Metadata name cannot be empty', resp.body)
 
     def test_check_metadata_non_utf8(self):
-        headers = {'X-Account-Meta-Foo': b'\xff'}
+        # Consciously using native "WSGI strings" in headers
+        headers = {'X-Account-Meta-Foo': '\xff'}
         resp = constraints.check_metadata(Request.blank(
             '/', headers=headers), 'account')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Metadata must be valid UTF-8', resp.body)
+        self.assertIn(b'Metadata must be valid UTF-8', resp.body)
 
-        headers = {b'X-Container-Meta-\xff': 'foo'}
+        headers = {'X-Container-Meta-\xff': 'foo'}
         resp = constraints.check_metadata(Request.blank(
             '/', headers=headers), 'container')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Metadata must be valid UTF-8', resp.body)
+        self.assertIn(b'Metadata must be valid UTF-8', resp.body)
         # Object's OK; its metadata isn't serialized as JSON
-        headers = {'X-Object-Meta-Foo': b'\xff'}
+        headers = {'X-Object-Meta-Foo': '\xff'}
         self.assertIsNone(constraints.check_metadata(Request.blank(
             '/', headers=headers), 'object'))
 
@@ -75,8 +76,8 @@ class TestConstraints(unittest.TestCase):
             '/', headers=headers), 'object')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
         self.assertIn(
-            ('X-Object-Meta-%s' % name).lower(), resp.body.lower())
-        self.assertIn('Metadata name too long', resp.body)
+            b'x-object-meta-%s' % name.encode('ascii'), resp.body.lower())
+        self.assertIn(b'Metadata name too long', resp.body)
 
     def test_check_metadata_value_length(self):
         value = 'a' * constraints.MAX_META_VALUE_LENGTH
@@ -89,10 +90,10 @@ class TestConstraints(unittest.TestCase):
         resp = constraints.check_metadata(Request.blank(
             '/', headers=headers), 'object')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('x-object-meta-name', resp.body.lower())
+        self.assertIn(b'x-object-meta-name', resp.body.lower())
         self.assertIn(
-            str(constraints.MAX_META_VALUE_LENGTH), resp.body)
-        self.assertIn('Metadata value longer than 256', resp.body)
+            str(constraints.MAX_META_VALUE_LENGTH).encode('ascii'), resp.body)
+        self.assertIn(b'Metadata value longer than 256', resp.body)
 
     def test_check_metadata_count(self):
         headers = {}
@@ -105,7 +106,7 @@ class TestConstraints(unittest.TestCase):
         resp = constraints.check_metadata(Request.blank(
             '/', headers=headers), 'object')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Too many metadata items', resp.body)
+        self.assertIn(b'Too many metadata items', resp.body)
 
     def test_check_metadata_size(self):
         headers = {}
@@ -132,7 +133,7 @@ class TestConstraints(unittest.TestCase):
         resp = constraints.check_metadata(Request.blank(
             '/', headers=headers), 'object')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Total metadata too large', resp.body)
+        self.assertIn(b'Total metadata too large', resp.body)
 
     def test_check_object_creation_content_length(self):
         headers = {'Content-Length': str(constraints.MAX_FILE_SIZE),
@@ -160,7 +161,7 @@ class TestConstraints(unittest.TestCase):
         resp = constraints.check_object_creation(Request.blank(
             '/', headers=headers), 'object_name')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Invalid Transfer-Encoding header value', resp.body)
+        self.assertIn(b'Invalid Transfer-Encoding header value', resp.body)
 
         headers = {'Content-Type': 'text/plain',
                    'X-Timestamp': str(time.time())}
@@ -174,7 +175,7 @@ class TestConstraints(unittest.TestCase):
         resp = constraints.check_object_creation(Request.blank(
             '/', headers=headers), 'object_name')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Invalid Content-Length header value', resp.body)
+        self.assertIn(b'Invalid Content-Length header value', resp.body)
 
         headers = {'Transfer-Encoding': 'gzip,chunked',
                    'Content-Type': 'text/plain',
@@ -195,7 +196,7 @@ class TestConstraints(unittest.TestCase):
         resp = constraints.check_object_creation(
             Request.blank('/', headers=headers), name)
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Object name length of %d longer than %d' %
+        self.assertIn(b'Object name length of %d longer than %d' %
                       (MAX_OBJECT_NAME_LENGTH + 1, MAX_OBJECT_NAME_LENGTH),
                       resp.body)
 
@@ -211,7 +212,7 @@ class TestConstraints(unittest.TestCase):
         resp = constraints.check_object_creation(
             Request.blank('/', headers=headers), 'object_name')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('No content type', resp.body)
+        self.assertIn(b'No content type', resp.body)
 
     def test_check_object_creation_bad_content_type(self):
         headers = {'Transfer-Encoding': 'chunked',
@@ -220,7 +221,7 @@ class TestConstraints(unittest.TestCase):
         resp = constraints.check_object_creation(
             Request.blank('/', headers=headers), 'object_name')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Content-Type', resp.body)
+        self.assertIn(b'Content-Type', resp.body)
 
     def test_check_object_creation_bad_delete_headers(self):
         headers = {'Transfer-Encoding': 'chunked',
@@ -230,7 +231,7 @@ class TestConstraints(unittest.TestCase):
         resp = constraints.check_object_creation(
             Request.blank('/', headers=headers), 'object_name')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Non-integer X-Delete-After', resp.body)
+        self.assertIn(b'Non-integer X-Delete-After', resp.body)
 
         t = str(int(time.time() - 60))
         headers = {'Transfer-Encoding': 'chunked',
@@ -240,7 +241,7 @@ class TestConstraints(unittest.TestCase):
         resp = constraints.check_object_creation(
             Request.blank('/', headers=headers), 'object_name')
         self.assertEqual(resp.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('X-Delete-At in past', resp.body)
+        self.assertIn(b'X-Delete-At in past', resp.body)
 
     def test_check_delete_headers(self):
         # x-delete-at value should be relative to the request timestamp rather
@@ -265,7 +266,7 @@ class TestConstraints(unittest.TestCase):
             constraints.check_delete_headers(
                 Request.blank('/', headers=headers))
         self.assertEqual(cm.exception.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Non-integer X-Delete-After', cm.exception.body)
+        self.assertIn(b'Non-integer X-Delete-After', cm.exception.body)
 
         headers = {'X-Delete-After': '60.1',
                    'X-Timestamp': ts.internal}
@@ -273,7 +274,7 @@ class TestConstraints(unittest.TestCase):
             constraints.check_delete_headers(
                 Request.blank('/', headers=headers))
         self.assertEqual(cm.exception.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Non-integer X-Delete-After', cm.exception.body)
+        self.assertIn(b'Non-integer X-Delete-After', cm.exception.body)
 
         headers = {'X-Delete-After': '-1',
                    'X-Timestamp': ts.internal}
@@ -281,7 +282,7 @@ class TestConstraints(unittest.TestCase):
             constraints.check_delete_headers(
                 Request.blank('/', headers=headers))
         self.assertEqual(cm.exception.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('X-Delete-After in past', cm.exception.body)
+        self.assertIn(b'X-Delete-After in past', cm.exception.body)
 
         headers = {'X-Delete-After': '0',
                    'X-Timestamp': ts.internal}
@@ -289,7 +290,7 @@ class TestConstraints(unittest.TestCase):
             constraints.check_delete_headers(
                 Request.blank('/', headers=headers))
         self.assertEqual(cm.exception.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('X-Delete-After in past', cm.exception.body)
+        self.assertIn(b'X-Delete-After in past', cm.exception.body)
 
         # x-delete-after = 0 disallowed when it results in x-delete-at equal to
         # the timestamp
@@ -299,7 +300,7 @@ class TestConstraints(unittest.TestCase):
             constraints.check_delete_headers(
                 Request.blank('/', headers=headers))
         self.assertEqual(cm.exception.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('X-Delete-After in past', cm.exception.body)
+        self.assertIn(b'X-Delete-After in past', cm.exception.body)
 
         # X-Delete-At
         delete_at = str(int(ts) + 100)
@@ -317,7 +318,7 @@ class TestConstraints(unittest.TestCase):
             constraints.check_delete_headers(
                 Request.blank('/', headers=headers))
         self.assertEqual(cm.exception.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Non-integer X-Delete-At', cm.exception.body)
+        self.assertIn(b'Non-integer X-Delete-At', cm.exception.body)
 
         delete_at = str(int(ts) + 100) + '.1'
         headers = {'X-Delete-At': delete_at,
@@ -326,7 +327,7 @@ class TestConstraints(unittest.TestCase):
             constraints.check_delete_headers(
                 Request.blank('/', headers=headers))
         self.assertEqual(cm.exception.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('Non-integer X-Delete-At', cm.exception.body)
+        self.assertIn(b'Non-integer X-Delete-At', cm.exception.body)
 
         delete_at = str(int(ts) - 1)
         headers = {'X-Delete-At': delete_at,
@@ -335,7 +336,7 @@ class TestConstraints(unittest.TestCase):
             constraints.check_delete_headers(
                 Request.blank('/', headers=headers))
         self.assertEqual(cm.exception.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('X-Delete-At in past', cm.exception.body)
+        self.assertIn(b'X-Delete-At in past', cm.exception.body)
 
         # x-delete-at disallowed when exactly equal to timestamp
         delete_at = str(int(ts))
@@ -345,7 +346,7 @@ class TestConstraints(unittest.TestCase):
             constraints.check_delete_headers(
                 Request.blank('/', headers=headers))
         self.assertEqual(cm.exception.status_int, HTTP_BAD_REQUEST)
-        self.assertIn('X-Delete-At in past', cm.exception.body)
+        self.assertIn(b'X-Delete-At in past', cm.exception.body)
 
     def test_check_delete_headers_removes_delete_after(self):
         ts = utils.Timestamp.now()
@@ -468,30 +469,45 @@ class TestConstraints(unittest.TestCase):
 
     def test_check_utf8(self):
         unicode_sample = u'\uc77c\uc601'
-        valid_utf8_str = unicode_sample.encode('utf-8')
-        invalid_utf8_str = unicode_sample.encode('utf-8')[::-1]
         unicode_with_null = u'abc\u0000def'
-        utf8_with_null = unicode_with_null.encode('utf-8')
 
-        for false_argument in [None,
-                               '',
-                               invalid_utf8_str,
-                               unicode_with_null,
-                               utf8_with_null]:
-            self.assertFalse(constraints.check_utf8(false_argument))
+        # Some false-y values
+        self.assertFalse(constraints.check_utf8(None))
+        self.assertFalse(constraints.check_utf8(''))
+        self.assertFalse(constraints.check_utf8(b''))
+        self.assertFalse(constraints.check_utf8(u''))
 
-        for true_argument in ['this is ascii and utf-8, too',
-                              unicode_sample,
-                              valid_utf8_str]:
-            self.assertTrue(constraints.check_utf8(true_argument))
+        # invalid utf8 bytes
+        self.assertFalse(constraints.check_utf8(
+            unicode_sample.encode('utf-8')[::-1]))
+        # unicode with null
+        self.assertFalse(constraints.check_utf8(unicode_with_null))
+        # utf8 bytes with null
+        self.assertFalse(constraints.check_utf8(
+            unicode_with_null.encode('utf8')))
+
+        self.assertTrue(constraints.check_utf8('this is ascii and utf-8, too'))
+        self.assertTrue(constraints.check_utf8(unicode_sample))
+        self.assertTrue(constraints.check_utf8(unicode_sample.encode('utf8')))
 
     def test_check_utf8_non_canonical(self):
-        self.assertFalse(constraints.check_utf8('\xed\xa0\xbc\xed\xbc\xb8'))
-        self.assertFalse(constraints.check_utf8('\xed\xa0\xbd\xed\xb9\x88'))
+        self.assertFalse(constraints.check_utf8(b'\xed\xa0\xbc\xed\xbc\xb8'))
+        self.assertTrue(constraints.check_utf8(u'\U0001f338'))
+        self.assertTrue(constraints.check_utf8(b'\xf0\x9f\x8c\xb8'))
+        self.assertTrue(constraints.check_utf8(u'\U0001f338'.encode('utf8')))
+        self.assertFalse(constraints.check_utf8(b'\xed\xa0\xbd\xed\xb9\x88'))
+        self.assertTrue(constraints.check_utf8(u'\U0001f648'))
 
     def test_check_utf8_lone_surrogates(self):
-        self.assertFalse(constraints.check_utf8('\xed\xa0\xbc'))
-        self.assertFalse(constraints.check_utf8('\xed\xb9\x88'))
+        self.assertFalse(constraints.check_utf8(b'\xed\xa0\xbc'))
+        self.assertFalse(constraints.check_utf8(u'\ud83c'))
+        self.assertFalse(constraints.check_utf8(b'\xed\xb9\x88'))
+        self.assertFalse(constraints.check_utf8(u'\ude48'))
+
+        self.assertFalse(constraints.check_utf8(u'\ud800'))
+        self.assertFalse(constraints.check_utf8(u'\udc00'))
+        self.assertFalse(constraints.check_utf8(u'\udcff'))
+        self.assertFalse(constraints.check_utf8(u'\udfff'))
 
     def test_validate_bad_meta(self):
         req = Request.blank(
@@ -500,8 +516,9 @@ class TestConstraints(unittest.TestCase):
                      'ab' * constraints.MAX_HEADER_SIZE})
         self.assertEqual(constraints.check_metadata(req, 'object').status_int,
                          HTTP_BAD_REQUEST)
-        self.assertIn('x-object-meta-hello', constraints.check_metadata(req,
-                      'object').body.lower())
+        resp = constraints.check_metadata(req, 'object')
+        self.assertIsNotNone(resp)
+        self.assertIn(b'x-object-meta-hello', resp.body.lower())
 
     def test_validate_constraints(self):
         c = constraints
@@ -537,7 +554,7 @@ class TestConstraints(unittest.TestCase):
                 constraints.check_container_format(
                     req, req.headers['X-Versions-Location'])
             self.assertTrue(cm.exception.body.startswith(
-                'Container name cannot'))
+                b'Container name cannot'))
 
     def test_valid_api_version(self):
         version = 'v1'
@@ -579,10 +596,10 @@ class TestConstraintsConfig(unittest.TestCase):
     def test_override_constraints(self):
         try:
             with tempfile.NamedTemporaryFile() as f:
-                f.write('[swift-constraints]\n')
+                f.write(b'[swift-constraints]\n')
                 # set everything to 1
                 for key in constraints.DEFAULT_CONSTRAINTS:
-                    f.write('%s = 1\n' % key)
+                    f.write(b'%s = 1\n' % key.encode('ascii'))
                 f.flush()
                 with mock.patch.object(utils, 'SWIFT_CONF_FILE', f.name):
                     constraints.reload_constraints()
@@ -603,10 +620,10 @@ class TestConstraintsConfig(unittest.TestCase):
     def test_reload_reset(self):
         try:
             with tempfile.NamedTemporaryFile() as f:
-                f.write('[swift-constraints]\n')
+                f.write(b'[swift-constraints]\n')
                 # set everything to 1
                 for key in constraints.DEFAULT_CONSTRAINTS:
-                    f.write('%s = 1\n' % key)
+                    f.write(b'%s = 1\n' % key.encode('ascii'))
                 f.flush()
                 with mock.patch.object(utils, 'SWIFT_CONF_FILE', f.name):
                     constraints.reload_constraints()
@@ -619,7 +636,7 @@ class TestConstraintsConfig(unittest.TestCase):
             # no constraints have been loaded from non-existent swift.conf
             self.assertFalse(constraints.SWIFT_CONSTRAINTS_LOADED)
             # no constraints are in OVERRIDE
-            self.assertEqual([], constraints.OVERRIDE_CONSTRAINTS.keys())
+            self.assertEqual([], list(constraints.OVERRIDE_CONSTRAINTS.keys()))
             # the EFFECTIVE constraints mirror DEFAULT
             self.assertEqual(constraints.EFFECTIVE_CONSTRAINTS,
                              constraints.DEFAULT_CONSTRAINTS)
diff --git a/tox.ini b/tox.ini
index b6d2db7885..9071675e3a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -38,6 +38,7 @@ commands =
       test/unit/cli/test_ringbuilder.py \
       test/unit/common/middleware/test_gatekeeper.py \
       test/unit/common/ring \
+      test/unit/common/test_constraints.py \
       test/unit/common/test_daemon.py \
       test/unit/common/test_exceptions.py \
       test/unit/common/test_header_key_dict.py \