diff --git a/nova/db/sqlalchemy/api.py b/nova/db/sqlalchemy/api.py
index 9213b36b3f58..52d25293a853 100644
--- a/nova/db/sqlalchemy/api.py
+++ b/nova/db/sqlalchemy/api.py
@@ -3018,8 +3018,19 @@ def _block_device_mapping_get_query(context, session=None):
     return model_query(context, models.BlockDeviceMapping, session=session)
 
 
+def _scrub_empty_str_values(dct, keys_to_scrub):
+    """
+    Remove any keys found in sequence keys_to_scrub from the dict
+    if they have the value ''.
+    """
+    for key in keys_to_scrub:
+        if key in dct and dct[key] == '':
+            del dct[key]
+
+
 @require_context
 def block_device_mapping_create(context, values):
+    _scrub_empty_str_values(values, ['volume_size'])
     bdm_ref = models.BlockDeviceMapping()
     bdm_ref.update(values)
     bdm_ref.save()
@@ -3027,6 +3038,7 @@ def block_device_mapping_create(context, values):
 
 @require_context
 def block_device_mapping_update(context, bdm_id, values):
+    _scrub_empty_str_values(values, ['volume_size'])
     _block_device_mapping_get_query(context).\
             filter_by(id=bdm_id).\
             update(values)
@@ -3034,6 +3046,7 @@ def block_device_mapping_update(context, bdm_id, values):
 
 @require_context
 def block_device_mapping_update_or_create(context, values):
+    _scrub_empty_str_values(values, ['volume_size'])
     session = get_session()
     with session.begin():
         result = _block_device_mapping_get_query(context, session=session).\
diff --git a/nova/tests/test_db_api.py b/nova/tests/test_db_api.py
index e298b7e03da3..a3317b218c66 100644
--- a/nova/tests/test_db_api.py
+++ b/nova/tests/test_db_api.py
@@ -19,6 +19,7 @@
 
 """Unit tests for the DB API."""
 
+import copy
 import datetime
 import types
 import uuid as stdlib_uuid
@@ -3344,6 +3345,22 @@ class BlockDeviceMappingTestCase(test.TestCase):
             if bdm['device_name'] == values['device_name']:
                 return bdm
 
+    def test_scrub_empty_str_values_no_effect(self):
+        values = {'volume_size': 5}
+        expected = copy.copy(values)
+        sqlalchemy_api._scrub_empty_str_values(values, ['volume_size'])
+        self.assertEqual(values, expected)
+
+    def test_scrub_empty_str_values_empty_string(self):
+        values = {'volume_size': ''}
+        sqlalchemy_api._scrub_empty_str_values(values, ['volume_size'])
+        self.assertEqual(values, {})
+
+    def test_scrub_empty_str_values_empty_unicode(self):
+        values = {'volume_size': u''}
+        sqlalchemy_api._scrub_empty_str_values(values, ['volume_size'])
+        self.assertEqual(values, {})
+
     def test_block_device_mapping_create(self):
         bdm = self._create_bdm({})
         self.assertFalse(bdm is None)