diff --git a/cinder/api/contrib/backups.py b/cinder/api/contrib/backups.py
index 8be8b1fb570..4cd9e2fa2cc 100644
--- a/cinder/api/contrib/backups.py
+++ b/cinder/api/contrib/backups.py
@@ -317,10 +317,10 @@ class BackupsController(wsgi.Controller):
             raise exc.HTTPNotFound(explanation=error.msg)
         except exception.VolumeSizeExceedsAvailableQuota as error:
             raise exc.HTTPRequestEntityTooLarge(
-                explanation=error.msg, headers={'Retry-After': 0})
+                explanation=error.msg, headers={'Retry-After': '0'})
         except exception.VolumeLimitExceeded as error:
             raise exc.HTTPRequestEntityTooLarge(
-                explanation=error.msg, headers={'Retry-After': 0})
+                explanation=error.msg, headers={'Retry-After': '0'})
 
         retval = self._view_builder.restore_summary(
             req, dict(new_restore))
diff --git a/cinder/api/contrib/volume_transfer.py b/cinder/api/contrib/volume_transfer.py
index b1358ebd8db..d5700ae08df 100644
--- a/cinder/api/contrib/volume_transfer.py
+++ b/cinder/api/contrib/volume_transfer.py
@@ -208,7 +208,7 @@ class VolumeTransferController(wsgi.Controller):
                                                          auth_key)
         except exception.VolumeSizeExceedsAvailableQuota as error:
             raise exc.HTTPRequestEntityTooLarge(
-                explanation=error.msg, headers={'Retry-After': 0})
+                explanation=error.msg, headers={'Retry-After': '0'})
         except exception.InvalidVolume as error:
             raise exc.HTTPBadRequest(explanation=error.msg)
 
diff --git a/cinder/exception.py b/cinder/exception.py
index adaa7554000..9a2b3b6b5ae 100644
--- a/cinder/exception.py
+++ b/cinder/exception.py
@@ -441,7 +441,7 @@ class NoMoreTargets(CinderException):
 class QuotaError(CinderException):
     message = _("Quota exceeded: code=%(code)s")
     code = 413
-    headers = {'Retry-After': 0}
+    headers = {'Retry-After': '0'}
     safe = True
 
 
diff --git a/cinder/tests/unit/api/middleware/test_faults.py b/cinder/tests/unit/api/middleware/test_faults.py
index e31fd97bcfb..f4761c06c7d 100644
--- a/cinder/tests/unit/api/middleware/test_faults.py
+++ b/cinder/tests/unit/api/middleware/test_faults.py
@@ -72,14 +72,14 @@ class TestFaults(test.TestCase):
         for request in requests:
             exc = webob.exc.HTTPRequestEntityTooLarge
             fault = wsgi.Fault(exc(explanation='sorry',
-                                   headers={'Retry-After': 4}))
+                                   headers={'Retry-After': '4'}))
             response = request.get_response(fault)
 
             expected = {
                 "overLimit": {
                     "message": "sorry",
                     "code": 413,
-                    "retryAfter": 4,
+                    "retryAfter": "4",
                 },
             }
             actual = jsonutils.loads(response.body)