diff --git a/swift/common/middleware/s3api/s3request.py b/swift/common/middleware/s3api/s3request.py
index b075c363e1..c8280aa502 100644
--- a/swift/common/middleware/s3api/s3request.py
+++ b/swift/common/middleware/s3api/s3request.py
@@ -375,6 +375,16 @@ class SigV4Mixin(object):
                           '/'.join(self.scope),
                           sha256(self._canonical_request()).hexdigest()])
 
+    def signature_does_not_match_kwargs(self):
+        kwargs = super(SigV4Mixin, self).signature_does_not_match_kwargs()
+        cr = self._canonical_request()
+        kwargs.update({
+            'canonical_request': cr,
+            'canonical_request_bytes': ' '.join(
+                format(ord(c), '02x') for c in cr),
+        })
+        return kwargs
+
 
 def get_request_class(env, s3_acl):
     """
@@ -875,6 +885,15 @@ class S3Request(swob.Request):
             buf.append(path)
         return '\n'.join(buf)
 
+    def signature_does_not_match_kwargs(self):
+        return {
+            'a_w_s_access_key_id': self.access_key,
+            'string_to_sign': self.string_to_sign,
+            'signature_provided': self.signature,
+            'string_to_sign_bytes': ' '.join(
+                format(ord(c), '02x') for c in self.string_to_sign),
+        }
+
     @property
     def controller_name(self):
         return self.controller.__name__[:-len('Controller')]
@@ -1211,7 +1230,8 @@ class S3Request(swob.Request):
         if status == HTTP_BAD_REQUEST:
             raise BadSwiftRequest(err_msg)
         if status == HTTP_UNAUTHORIZED:
-            raise SignatureDoesNotMatch()
+            raise SignatureDoesNotMatch(
+                **self.signature_does_not_match_kwargs())
         if status == HTTP_FORBIDDEN:
             raise AccessDenied()
 
@@ -1334,7 +1354,8 @@ class S3AclRequest(S3Request):
         sw_resp = sw_req.get_response(app)
 
         if not sw_req.remote_user:
-            raise SignatureDoesNotMatch()
+            raise SignatureDoesNotMatch(
+                **self.signature_does_not_match_kwargs())
 
         _, self.account, _ = split_path(sw_resp.environ['PATH_INFO'],
                                         2, 3, True)
diff --git a/test/unit/common/middleware/s3api/__init__.py b/test/unit/common/middleware/s3api/__init__.py
index 7963e615c3..c4271ebd3a 100644
--- a/test/unit/common/middleware/s3api/__init__.py
+++ b/test/unit/common/middleware/s3api/__init__.py
@@ -107,7 +107,7 @@ class S3ApiTestCase(unittest.TestCase):
         return elem.find('./Message').text
 
     def _test_method_error(self, method, path, response_class, headers={},
-                           env={}):
+                           env={}, expected_xml_tags=None):
         if not path.startswith('/'):
             path = '/' + path  # add a missing slash before the path
 
@@ -121,6 +121,10 @@ class S3ApiTestCase(unittest.TestCase):
         env.update({'REQUEST_METHOD': method})
         req = swob.Request.blank(path, environ=env, headers=headers)
         status, headers, body = self.call_s3api(req)
+        if expected_xml_tags is not None:
+            elem = fromstring(body, 'Error')
+            self.assertEqual(set(expected_xml_tags),
+                             {x.tag for x in elem})
         return self._get_error_code(body)
 
     def get_date_header(self):
diff --git a/test/unit/common/middleware/s3api/helpers.py b/test/unit/common/middleware/s3api/helpers.py
index 63a4839800..8cf1b7963c 100644
--- a/test/unit/common/middleware/s3api/helpers.py
+++ b/test/unit/common/middleware/s3api/helpers.py
@@ -35,6 +35,7 @@ class FakeSwift(object):
         # mapping of (method, path) --> (response class, headers, body)
         self._responses = {}
         self.s3_acl = s3_acl
+        self.remote_user = 'authorized'
 
     def _fake_auth_middleware(self, env):
         if 'swift.authorize_override' in env:
@@ -50,7 +51,8 @@ class FakeSwift(object):
         path = env['PATH_INFO']
         env['PATH_INFO'] = path.replace(tenant_user, 'AUTH_' + tenant)
 
-        env['REMOTE_USER'] = 'authorized'
+        if self.remote_user:
+            env['REMOTE_USER'] = self.remote_user
 
         if env['REQUEST_METHOD'] == 'TEST':
 
diff --git a/test/unit/common/middleware/s3api/test_obj.py b/test/unit/common/middleware/s3api/test_obj.py
index fdddb0ecd4..a88c6476d6 100644
--- a/test/unit/common/middleware/s3api/test_obj.py
+++ b/test/unit/common/middleware/s3api/test_obj.py
@@ -306,6 +306,17 @@ class TestS3ApiObj(S3ApiTestCase):
     def test_object_GET(self):
         self._test_object_GETorHEAD('GET')
 
+    @s3acl(s3acl_only=True)
+    def test_object_GET_with_s3acl_and_unknown_user(self):
+        self.swift.remote_user = None
+        req = Request.blank('/bucket/object',
+                            environ={'REQUEST_METHOD': 'GET'},
+                            headers={'Authorization': 'AWS test:tester:hmac',
+                                     'Date': self.get_date_header()})
+        status, headers, body = self.call_s3api(req)
+        self.assertEqual(status, '403 Forbidden')
+        self.assertEqual(self._get_error_code(body), 'SignatureDoesNotMatch')
+
     @s3acl(s3acl_only=True)
     def test_object_GET_with_s3acl_and_keystone(self):
         # for passing keystone authentication root
diff --git a/test/unit/common/middleware/s3api/test_service.py b/test/unit/common/middleware/s3api/test_service.py
index 5571e56a1f..431386d7cc 100644
--- a/test/unit/common/middleware/s3api/test_service.py
+++ b/test/unit/common/middleware/s3api/test_service.py
@@ -50,7 +50,10 @@ class TestS3ApiService(S3ApiTestCase):
         self.setup_buckets()
 
     def test_service_GET_error(self):
-        code = self._test_method_error('GET', '', swob.HTTPUnauthorized)
+        code = self._test_method_error(
+            'GET', '', swob.HTTPUnauthorized, expected_xml_tags=(
+                'Code', 'Message', 'AWSAccessKeyId', 'StringToSign',
+                'StringToSignBytes', 'SignatureProvided'))
         self.assertEqual(code, 'SignatureDoesNotMatch')
         code = self._test_method_error('GET', '', swob.HTTPForbidden)
         self.assertEqual(code, 'AccessDenied')