diff --git a/anki/decks.py b/anki/decks.py
index 029a7ae6a..6d3a58b59 100644
--- a/anki/decks.py
+++ b/anki/decks.py
@@ -2,7 +2,7 @@
 # Copyright: Damien Elmes <anki@ichi2.net>
 # License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
-import copy
+import copy, operator
 from anki.utils import intTime, ids2str, json
 from anki.hooks import runHook
 from anki.consts import *
@@ -473,6 +473,34 @@ class DeckManager:
                 actv.append((g['name'], g['id']))
         return actv
 
+    def childDids(self, did, childMap):
+        def gather(node, arr):
+            for did, child in node.items():
+                arr.append(did)
+                gather(child, arr)
+
+        arr = []
+        gather(childMap[did], arr)
+        return arr
+
+    def childMap(self):
+        nameMap = self.nameMap()
+        childMap = {}
+
+        # go through all decks, sorted by name
+        for deck in sorted(self.all(), key=operator.itemgetter("name")):
+            node = {}
+            childMap[deck['id']] = node
+
+            # add note to immediate parent
+            parts = deck['name'].split("::")
+            if len(parts) > 1:
+                immediateParent = "::".join(parts[:-1])
+                pid = nameMap[immediateParent]['id']
+                childMap[pid][deck['id']] = node
+
+        return childMap
+
     def parents(self, did, nameMap=None):
         "All parents of did."
         # get parent and grandparent names
diff --git a/anki/schedv2.py b/anki/schedv2.py
index 8480b3b27..43c8092ef 100644
--- a/anki/schedv2.py
+++ b/anki/schedv2.py
@@ -215,6 +215,7 @@ order by due""" % self._deckLimit(),
                 return None
             parts = parts[:-1]
             return "::".join(parts)
+        childMap = self.col.decks.childMap()
         for deck in decks:
             # if we've already seen the exact same deck name, remove the
             # invalid duplicate and reload
@@ -240,7 +241,7 @@ order by due""" % self._deckLimit(),
             else:
                 plim = None
             rlim = self._deckRevLimitSingle(deck, parentLimit=plim)
-            rev = self._revForDeck(deck['id'], rlim)
+            rev = self._revForDeck(deck['id'], rlim, childMap)
             # save to list
             data.append([deck['name'], deck['id'], rev, lrn, new])
             # add deck as a parent
@@ -749,8 +750,8 @@ and due <= ? limit ?)""",
                 lim = min(lim, self._deckRevLimitSingle(parent, parentLimit=lim))
             return lim
 
-    def _revForDeck(self, did, lim):
-        dids = [did] + [x[1] for x in self.col.decks.children(did)]
+    def _revForDeck(self, did, lim, childMap):
+        dids = [did] + self.col.decks.childDids(did, childMap)
         lim = min(lim, self.reportLimit)
         return self.col.db.scalar(
             """