diff --git a/lib/groupdate/magic.rb b/lib/groupdate/magic.rb
index 0fe6253..6f2bb31 100644
--- a/lib/groupdate/magic.rb
+++ b/lib/groupdate/magic.rb
@@ -72,18 +72,11 @@ module Groupdate
       if options[:series] == false
         group
       else
-        relation =
-          if time_range.is_a?(Range)
-            # doesn't matter whether we include the end of a ... range - it will be excluded later
-            group.where("#{column} >= ? AND #{column} <= ?", time_range.first, time_range.last)
-          else
-            group.where("#{column} IS NOT NULL")
-          end
-
         # TODO do not change object state
         @group_index = group.group_values.size - 1
+        @column = column
 
-        Groupdate::Series.new(self, relation)
+        Groupdate::Series.new(self, group)
       end
     end
 
@@ -111,6 +104,16 @@ module Groupdate
           lambda{|k| (k.is_a?(String) ? utc.parse(k) : k.to_time).in_time_zone(time_zone) }
         end
 
+      if !options[:carry_forward]
+        relation =
+          if time_range.is_a?(Range)
+            # doesn't matter whether we include the end of a ... range - it will be excluded later
+            relation.where("#{@column} >= ? AND #{@column} <= ?", time_range.first, time_range.last)
+          else
+            relation.where("#{@column} IS NOT NULL")
+          end
+      end
+
       count =
         begin
           if method == :custom
diff --git a/lib/groupdate/series.rb b/lib/groupdate/series.rb
index 97a1493..d81d2c4 100644
--- a/lib/groupdate/series.rb
+++ b/lib/groupdate/series.rb
@@ -10,7 +10,7 @@ module Groupdate
     def cumulative_sum
       magic.options[:carry_forward] = true
       sql =
-        if magic.send(:postgresql?, connection.adapter_name)
+        if magic.send(:postgresql?, relation.connection.adapter_name)
           "SUM(COUNT(id)) OVER (ORDER BY #{relation.group_values[0]})::integer"
         else
           raise "`cumulative_sum` not supported with MySQL"
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 46d8b14..bd9ca00 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -641,11 +641,10 @@ module TestGroupdate
     create_user "2013-05-01 00:00:00 UTC"
     create_user "2013-05-01 00:00:00 UTC"
     expected = {
-      utc.parse("2012-01-01 00:00:00 UTC") => 1,
       utc.parse("2013-01-01 00:00:00 UTC") => 3,
       utc.parse("2014-01-01 00:00:00 UTC") => 3
     }
-    assert_equal expected, User.group_by_year(:created_at, last: 3).cumulative_sum
+    assert_equal expected, User.group_by_year(:created_at, last: 2).cumulative_sum
   end
 
   # helpers
--
libgit2 0.21.0