diff --git a/nova/tests/unit/virt/libvirt/test_imagebackend.py b/nova/tests/unit/virt/libvirt/test_imagebackend.py
index a76c4f60bd3c..013c73a06b2a 100644
--- a/nova/tests/unit/virt/libvirt/test_imagebackend.py
+++ b/nova/tests/unit/virt/libvirt/test_imagebackend.py
@@ -1558,11 +1558,28 @@ class RbdTestCase(_ImageTestCase, test.NoDBTestCase):
             ["server1:1899", "server2:1920"]),
                          model)
 
+    @mock.patch.object(rbd_utils.RBDDriver, 'parent_info')
     @mock.patch.object(rbd_utils.RBDDriver, 'flatten')
-    def test_flatten(self, mock_flatten):
+    def test_flatten(self, mock_flatten, mock_parent_info):
         image = self.image_class(self.INSTANCE, self.NAME)
         image.flatten()
         mock_flatten.assert_called_once_with(image.rbd_name, pool=self.POOL)
+        mock_parent_info.assert_called_once_with(
+            image.rbd_name, pool=self.POOL)
+
+    @mock.patch.object(imagebackend, 'LOG')
+    @mock.patch.object(rbd_utils.RBDDriver, 'parent_info')
+    @mock.patch.object(rbd_utils.RBDDriver, 'flatten')
+    def test_flatten_already_flat(
+            self, mock_flatten, mock_parent_info, mock_log):
+        mock_parent_info.side_effect = exception.ImageUnacceptable(
+            image_id=1, reason='foo')
+        image = self.image_class(self.INSTANCE, self.NAME)
+        image.flatten()
+        mock_log.debug.assert_called_once()
+        mock_flatten.assert_not_called()
+        mock_parent_info.assert_called_once_with(
+            image.rbd_name, pool=self.POOL)
 
     def test_import_file(self):
         image = self.image_class(self.INSTANCE, self.NAME)
diff --git a/nova/virt/libvirt/imagebackend.py b/nova/virt/libvirt/imagebackend.py
index d185b7e1eb2a..5a7877b77801 100644
--- a/nova/virt/libvirt/imagebackend.py
+++ b/nova/virt/libvirt/imagebackend.py
@@ -969,7 +969,17 @@ class Rbd(Image):
                                           reason=reason)
 
     def flatten(self):
-        self.driver.flatten(self.rbd_name, pool=self.pool)
+        # NOTE(vdrok): only flatten images if they are not already flattened,
+        # meaning that parent info is present
+        try:
+            self.driver.parent_info(self.rbd_name, pool=self.pool)
+        except exception.ImageUnacceptable:
+            LOG.debug(
+                "Image %(img)s from pool %(pool)s has no parent info, "
+                "consider it already flat", {
+                    'img': self.rbd_name, 'pool': self.pool})
+        else:
+            self.driver.flatten(self.rbd_name, pool=self.pool)
 
     def get_model(self, connection):
         secret = None