diff --git a/placement/db/sqlalchemy/alembic/versions/b5c396305c25_block_on_null_consumer.py b/placement/db/sqlalchemy/alembic/versions/b5c396305c25_block_on_null_consumer.py
new file mode 100644
index 000000000..75044c80c
--- /dev/null
+++ b/placement/db/sqlalchemy/alembic/versions/b5c396305c25_block_on_null_consumer.py
@@ -0,0 +1,50 @@
+#    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.
+
+"""Block on null consumer
+
+Revision ID: b5c396305c25
+Revises: 611cd6dffd7b
+Create Date: 2019-06-11 16:30:04.114287
+
+"""
+from alembic import context
+import sqlalchemy as sa
+from sqlalchemy import func as sqlfunc
+
+
+# revision identifiers, used by Alembic.
+revision = 'b5c396305c25'
+down_revision = '611cd6dffd7b'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    connection = context.get_bind()
+    metadata = sa.MetaData(bind=connection)
+    consumers = sa.Table('consumers', metadata, autoload=True)
+    allocations = sa.Table('allocations', metadata, autoload=True)
+    alloc_to_consumer = sa.outerjoin(
+        allocations, consumers,
+        allocations.c.consumer_id == consumers.c.uuid)
+    cols = [
+        sqlfunc.count(),
+    ]
+    sel = sa.select(cols)
+    sel = sel.select_from(alloc_to_consumer)
+    sel = sel.where(consumers.c.id.is_(None))
+
+    if connection.scalar(sel):
+        raise Exception('There is at least one allocation record which is '
+                        'missing a consumer record. Run the "placement-manage '
+                        'db online_data_migrations" command.')
diff --git a/placement/tests/functional/db/test_migrations.py b/placement/tests/functional/db/test_migrations.py
index 7b2b589d6..79058ce28 100644
--- a/placement/tests/functional/db/test_migrations.py
+++ b/placement/tests/functional/db/test_migrations.py
@@ -193,6 +193,39 @@ class MigrationCheckersMixin(object):
         # Re-run the upgrade and it should be OK.
         self.migration_api.upgrade('611cd6dffd7b')
 
+    def test_block_on_missing_consumer(self):
+        """Upgrades the schema to b4ed3a175331 (initial), injects an allocation
+        without a corresponding consumer record and then tries to upgrade to
+        head which should fail on the b5c396305c25 blocker migration.
+        """
+        # Upgrade to populate the schema.
+        self.migration_api.upgrade('b4ed3a175331')
+        # Now insert a resource provider to build off
+        rps = db_utils.get_table(self.engine, 'resource_providers')
+        rp_id = rps.insert(values={
+            'name': 'fake-rp-name', 'uuid': uuids.rp_uuid,
+            'root_provider_id': 1
+        }).execute().inserted_primary_key[0]
+        # Now insert an allocation
+        allocations = db_utils.get_table(self.engine, 'allocations')
+        allocations.insert(values={
+            'resource_provider_id': rp_id, 'resource_class_id': 1,
+            'used': 5, 'consumer_id': uuids.consumer1
+        }).execute().inserted_primary_key[0]
+        # Now run the blocker migration and it should raise an error.
+        ex = self.assertRaises(  # noqa H202
+            Exception, self.migration_api.upgrade, 'b5c396305c25')
+        # Make sure it's the error we expect.
+        self.assertIn('There is at least one allocation record which is '
+                      'missing a consumer record.',
+                      six.text_type(ex))
+        # Add a (faked) consumer record and try again
+        consumers = db_utils.get_table(self.engine, 'consumers')
+        consumers.insert(values={
+            'uuid': uuids.consumer1, 'project_id': 1, 'user_id': 1
+        }).execute().inserted_primary_key[0]
+        self.migration_api.upgrade('b5c396305c25')
+
 
 class PlacementOpportunisticFixture(object):
     def get_enginefacade(self):