diff --git a/firedrake/mg/utils.py b/firedrake/mg/utils.py
index c716a99676..353741e464 100644
--- a/firedrake/mg/utils.py
+++ b/firedrake/mg/utils.py
@@ -8,23 +8,28 @@
 from firedrake.cython import mgimpl as impl
 
 
-def get_or_set_mg_hierarchy_map_cache(cache_dict, entity_dofs_key,
-        create_map_on_cpu):
+def get_or_set_mg_hierarchy_map_cache(cache_dict, entity_dofs_key, create_map_on_cpu):
     """
     :arg cache_dict: An instance of :class:`dict` that maps from tuple
         ``(entity_dofs_key, compute_backend)`` to the corresponding map.
-    :arg create_host_map: A callable that takes no argument and returns the map
+    :arg create_map_on_cpu: A callable that takes no argument and returns the map
         on the CPU backend.
     :returns map: An instance of :class:`pyop2.base.Map`.
     """
     try:
         return cache_dict[(entity_dofs_key, op2.compute_backend)]
     except KeyError:
+
         from pyop2.sequential import cpu_backend
-        host_map = cache_dict.setdefault((entity_dofs_key,
-            cpu_backend), create_map_on_cpu())
-        return cache_dict.setdefault((entity_dofs_key, op2.compute_backend),
-                op2.compute_backend.Map(host_map))
+        if (entity_dofs_key, cpu_backend) not in cache_dict:
+            cache_dict[(entity_dofs_key, cpu_backend)] = create_map_on_cpu()
+
+        map_on_cpu = cache_dict[(entity_dofs_key, cpu_backend)]
+
+        if (entity_dofs_key, op2.compute_backend) not in cache_dict:
+            cache_dict[(entity_dofs_key, op2.compute_backend)] = op2.compute_backend.Map(map_on_cpu)
+
+        return cache_dict[(entity_dofs_key, op2.compute_backend)]
 
 
 def fine_node_to_coarse_node_map(Vf, Vc):