diff --git a/nova/db/sqlalchemy/api_migrations/migrate_repo/versions/020_block_device_mappings_mediumtext.py b/nova/db/sqlalchemy/api_migrations/migrate_repo/versions/020_block_device_mappings_mediumtext.py
new file mode 100644
index 000000000000..f51455a10934
--- /dev/null
+++ b/nova/db/sqlalchemy/api_migrations/migrate_repo/versions/020_block_device_mappings_mediumtext.py
@@ -0,0 +1,24 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from sqlalchemy import MetaData
+from sqlalchemy import Table
+
+from nova.db.sqlalchemy import api_models
+
+
+def upgrade(migrate_engine):
+    meta = MetaData()
+    meta.bind = migrate_engine
+
+    build_requests = Table('build_requests', meta, autoload=True)
+    build_requests.c.block_device_mappings.alter(type=api_models.MediumText())
diff --git a/nova/db/sqlalchemy/api_models.py b/nova/db/sqlalchemy/api_models.py
index 2b149e76411f..d5dd7ecfce0c 100644
--- a/nova/db/sqlalchemy/api_models.py
+++ b/nova/db/sqlalchemy/api_models.py
@@ -14,6 +14,7 @@
 from oslo_db.sqlalchemy import models
 from sqlalchemy import Boolean
 from sqlalchemy import Column
+from sqlalchemy.dialects.mysql import MEDIUMTEXT
 from sqlalchemy import Enum
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy import Float
@@ -28,6 +29,10 @@ from sqlalchemy import Text
 from sqlalchemy import Unicode
 
 
+def MediumText():
+    return Text().with_variant(MEDIUMTEXT(), 'mysql')
+
+
 class _NovaAPIBase(models.ModelBase, models.TimestampMixin):
     pass
 
@@ -236,7 +241,7 @@ class BuildRequest(API_BASE):
     instance_uuid = Column(String(36))
     project_id = Column(String(255), nullable=False)
     instance = Column(Text)
-    block_device_mappings = Column(Text)
+    block_device_mappings = Column(MediumText())
     # TODO(alaski): Drop these from the db in Ocata
     # columns_to_drop = ['request_spec_id', 'user_id', 'display_name',
     #         'instance_metadata', 'progress', 'vm_state', 'task_state',
diff --git a/nova/tests/functional/db/api/test_migrations.py b/nova/tests/functional/db/api/test_migrations.py
index 616ffe3b0fe5..968f1f2f42a5 100644
--- a/nova/tests/functional/db/api/test_migrations.py
+++ b/nova/tests/functional/db/api/test_migrations.py
@@ -445,6 +445,23 @@ class NovaAPIMigrationsWalk(test_migrations.WalkVersionsMixin):
         self.assertColumnExists(engine, 'build_requests',
                                 'block_device_mappings')
 
+    def _pre_upgrade_020(self, engine):
+        build_requests = db_utils.get_table(engine, 'build_requests')
+        fake_build_req = {'id': 2020,
+                          'project_id': 'fake_proj_id',
+                          'block_device_mappings': 'fake_BDM'}
+        build_requests.insert().execute(fake_build_req)
+
+    def _check_020(self, engine, data):
+        build_requests = db_utils.get_table(engine, 'build_requests')
+        if engine.name == 'mysql':
+            self.assertIsInstance(build_requests.c.block_device_mappings.type,
+                                  sqlalchemy.dialects.mysql.MEDIUMTEXT)
+
+        fake_build_req = build_requests.select(
+            build_requests.c.id == 2020).execute().first()
+        self.assertEqual('fake_BDM', fake_build_req.block_device_mappings)
+
 
 class TestNovaAPIMigrationsWalkSQLite(NovaAPIMigrationsWalk,
                                       test_base.DbTestCase,