diff --git a/nova/cmd/manage.py b/nova/cmd/manage.py
index 356edc295489..57b68a2849e5 100644
--- a/nova/cmd/manage.py
+++ b/nova/cmd/manage.py
@@ -1257,7 +1257,7 @@ class CellV2Commands(object):
           metavar='<database_connection>',
           help='The database connection url for cell0. '
                'This is optional. If not provided, a standard database '
-               'connection will be used based on the API database connection '
+               'connection will be used based on the main database connection '
                'from the Nova configuration.'
          )
     def map_cell0(self, database_connection=None):
@@ -1272,11 +1272,11 @@ class CellV2Commands(object):
         """
         def cell0_default_connection():
             # If no database connection is provided one is generated
-            # based on the API database connection url.
+            # based on the database connection url.
             # The cell0 database will use the same database scheme and
-            # netloc as the API database, with a related path.
+            # netloc as the main database, with a related path.
             scheme, netloc, path, query, fragment = \
-                urlparse.urlsplit(CONF.api_database.connection)
+                urlparse.urlsplit(CONF.database.connection)
             root, ext = os.path.splitext(path)
             path = root + "_cell0" + ext
             return urlparse.urlunsplit((scheme, netloc, path, query,
diff --git a/nova/tests/unit/test_nova_manage.py b/nova/tests/unit/test_nova_manage.py
index 62197a8eab17..126835456ec5 100644
--- a/nova/tests/unit/test_nova_manage.py
+++ b/nova/tests/unit/test_nova_manage.py
@@ -1114,22 +1114,22 @@ class CellV2CommandsTestCase(test.TestCase):
 
     def test_map_cell0_default_database(self):
         CONF.set_default('connection',
-                         'fake://netloc/nova_api',
-                         group='api_database')
+                         'fake://netloc/nova',
+                         group='database')
         ctxt = context.RequestContext()
         self.commands.map_cell0()
         cell_mapping = objects.CellMapping.get_by_uuid(ctxt,
                 objects.CellMapping.CELL0_UUID)
         self.assertEqual('cell0', cell_mapping.name)
         self.assertEqual('none:///', cell_mapping.transport_url)
-        self.assertEqual('fake://netloc/nova_api_cell0',
+        self.assertEqual('fake://netloc/nova_cell0',
                          cell_mapping.database_connection)
 
     def _test_migrate_simple_command(self, cell0_sync_fail=False):
         ctxt = context.RequestContext()
         CONF.set_default('connection',
-                         'fake://netloc/nova_api',
-                         group='api_database')
+                         'fake://netloc/nova',
+                         group='database')
         values = {
                 'vcpus': 4,
                 'memory_mb': 4096,
@@ -1168,7 +1168,7 @@ class CellV2CommandsTestCase(test.TestCase):
                 objects.CellMapping.CELL0_UUID)
         self.assertEqual('cell0', cell_mapping.name)
         self.assertEqual('none:///', cell_mapping.transport_url)
-        self.assertEqual('fake://netloc/nova_api_cell0',
+        self.assertEqual('fake://netloc/nova_cell0',
                          cell_mapping.database_connection)
 
         # Verify the cell mapping
diff --git a/releasenotes/notes/cells-single-migration-command-0e98d66e31e02a50.yaml b/releasenotes/notes/cells-single-migration-command-0e98d66e31e02a50.yaml
index def0454664b1..c92d2ef6ef9c 100644
--- a/releasenotes/notes/cells-single-migration-command-0e98d66e31e02a50.yaml
+++ b/releasenotes/notes/cells-single-migration-command-0e98d66e31e02a50.yaml
@@ -10,4 +10,9 @@ upgrade:
     The new command is
     "nova-manage cell_v2 simple_cell_setup --transport_url <transport_url>"
     where transport_url is the connection information for the current message
-    queue used by Nova.
+    queue used by Nova. Operators must create a new database for cell0 before
+    running `cell_v2 simple_cell_setup`. The simple cell setup command expects
+    the name of the cell0 database to be `<main database name>_cell0` as it
+    will create a cell mapping for cell0 based on the main database connection,
+    sync the cell0 database, and associate existing hosts and instances with
+    the single cell.
diff --git a/releasenotes/notes/fix-default-cell0-db-connection-f9717053cc34778e.yaml b/releasenotes/notes/fix-default-cell0-db-connection-f9717053cc34778e.yaml
new file mode 100644
index 000000000000..d4f73498a415
--- /dev/null
+++ b/releasenotes/notes/fix-default-cell0-db-connection-f9717053cc34778e.yaml
@@ -0,0 +1,10 @@
+---
+fixes:
+  - |
+    The ``nova-manage cell_v2 simple_cell_setup`` command now creates the
+    default cell0 database connection using the ``[database]`` connection
+    configuration option rather than the ``[api_database]`` connection. The
+    cell0 database schema is the `main` database, i.e. the `instances` table,
+    rather than the `api` database schema. In other words, the cell0 database
+    would be called something like ``nova_cell0`` rather than
+    ``nova_api_cell0``.
\ No newline at end of file