diff --git a/CHANGES.rst b/CHANGES.rst
index 489fabc5..59172ceb 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -18,10 +18,14 @@ Bug fixes
 - Fix rewriting of query to avoid wrong optimization of CompositeIndex.
   (`#59 <https://github.com/zopefoundation/Products.ZCatalog/issues/59>`_)
 
-- Consolidate code for general usage of ``UnIndex._convert`` method to
-  avoid unnecessary doubling of code.
+- Consistent use of ``UnIndex._convert`` method to avoid unnecessary
+  doubling of code.
   (`#69 <https://github.com/zopefoundation/Products.ZCatalog/issues/69>`_)
 
+- Fix performance issue of ``valueindexes`` method for catalogs with
+  many indexed objects
+  (`#39 <https://github.com/zopefoundation/Products.ZCatalog/issues/39>`_)
+
 
 4.4 (2019-03-08)
 ----------------
diff --git a/src/Products/PluginIndexes/BooleanIndex/BooleanIndex.py b/src/Products/PluginIndexes/BooleanIndex/BooleanIndex.py
index f665f316..6ab2916b 100644
--- a/src/Products/PluginIndexes/BooleanIndex/BooleanIndex.py
+++ b/src/Products/PluginIndexes/BooleanIndex/BooleanIndex.py
@@ -238,6 +238,31 @@ def items(self):
         items.append((not bool(indexed), false))
         return items
 
+    def uniqueValues(self, name=None, withLengths=0):
+        """returns the unique values for name
+
+        if withLengths is true, returns a sequence of
+        tuples of (value, length)
+        """
+        if name is None:
+            name = self.id
+        elif name != self.id:
+            return
+
+        indexed = bool(self._index_value)
+        unique_values = (indexed, not indexed)
+        if not withLengths:
+            for key in unique_values:
+                yield key
+        else:
+            for key in unique_values:
+                ilen = len(self._index)
+                if key is indexed:
+                    yield (key, ilen)
+                else:
+                    ulen = len(self._unindex)
+                    yield (key, ulen - ilen)
+
 
 manage_addBooleanIndexForm = DTMLFile('dtml/addBooleanIndex', globals())
 
diff --git a/src/Products/ZCatalog/plan.py b/src/Products/ZCatalog/plan.py
index fec58654..1b88046b 100644
--- a/src/Products/ZCatalog/plan.py
+++ b/src/Products/ZCatalog/plan.py
@@ -25,6 +25,7 @@
 from zope.dottedname.resolve import resolve
 
 from Products.PluginIndexes.interfaces import IUniqueValueIndex
+from Products.PluginIndexes.interfaces import IDateRangeIndex
 
 
 MAX_DISTINCT_VALUES = 10
@@ -191,34 +192,33 @@ def valueindexes(self):
         # in the report key. The number of unique values for the index needs to
         # be lower than the MAX_DISTINCT_VALUES watermark.
 
-        # TODO: Ideally who would only consider those indexes with a small
+        # Ideally who would only consider those indexes with a small
         # number of unique values, where the number of items for each value
         # differs a lot. If the number of items per value is similar, the
-        # duration of a query is likely similar as well.
+        # duration of a query is likely similar as well. However, calculating
+        # all the value indexes with the number of items per value is
+        # quite slow. Therefore, we do not make this distinction.
         value_indexes = PriorityMap.get_entry(self.cid, VALUE_INDEX_KEY)
         if isinstance(value_indexes, (frozenset, set)):
-            # Calculating all the value indexes is quite slow, so we do this
-            # once for the first query. Since this is an optimization only,
-            # slightly outdated results based on index changes in the running
-            # process can be ignored.
+            # Since this is an optimization only, slightly outdated results
+            # based on index changes in the running process can be ignored.
             return value_indexes
 
         value_indexes = set()
         for name, index in indexes.items():
             if IUniqueValueIndex.providedBy(index):
-                values = index.uniqueValues()
-                i = 0
-                for value in values:
-                    # the total number of unique values might be large and
-                    # expensive to load, so we only check if we can get
-                    # more than MAX_DISTINCT_VALUES
-                    if i >= MAX_DISTINCT_VALUES:
-                        break
-                    i += 1
-                if i > 0 and i < MAX_DISTINCT_VALUES:
-                    # Only consider indexes which actually return a number
-                    # greater than zero
-                    value_indexes.add(name)
+
+                # DateRangeIndex is unsuitable for this purpose
+                if IDateRangeIndex.providedBy(index):
+                    continue
+
+                # the size of an UniqueValueIndex is typically equal to the
+                # number of unique values
+                isize = index.indexSize()
+                if isize >= MAX_DISTINCT_VALUES:
+                    continue
+
+                value_indexes.add(name)
 
         value_indexes = frozenset(value_indexes)
         PriorityMap.set_entry(self.cid, VALUE_INDEX_KEY, value_indexes)
diff --git a/src/Products/ZCatalog/tests/test_plan.py b/src/Products/ZCatalog/tests/test_plan.py
index 6c72b0a6..ba3f48f1 100644
--- a/src/Products/ZCatalog/tests/test_plan.py
+++ b/src/Products/ZCatalog/tests/test_plan.py
@@ -326,7 +326,7 @@ def _make_plan(self, catalog):
     def test_uniquevalues(self):
         zcat = self._make_catalog()
         indexes = zcat._catalog.indexes
-        self.assertEqual(len(list(indexes['big'].uniqueValues())), 3)
+        self.assertEqual(len(list(indexes['big'].uniqueValues())), 2)
         self.assertEqual(len(list(indexes['date'].uniqueValues())), 0)
         self.assertEqual(len(list(indexes['date'].uniqueValues('start'))), 9)
         self.assertEqual(len(list(indexes['date'].uniqueValues('end'))), 9)