diff --git a/activerecord/lib/active_record/association_preload.rb b/activerecord/lib/active_record/association_preload.rb
index 61fa34a..ae064ec 100644
--- a/activerecord/lib/active_record/association_preload.rb
+++ b/activerecord/lib/active_record/association_preload.rb
@@ -220,12 +220,16 @@ module ActiveRecord
           klass_name, id_map = *klass_and_id
           klass = klass_name.constantize
 
+          # do not find if there are no ids
+          uniq_ids = id_map.keys.uniq
+          next if uniq_ids.empty?
+
           table_name = klass.quoted_table_name
           primary_key = klass.primary_key
           conditions = "#{table_name}.#{connection.quote_column_name(primary_key)} IN (?)"
           conditions << append_conditions(options, preload_options)
           column_type = klass.columns.detect{|c| c.name == primary_key}.type
-          ids = id_map.keys.uniq.map do |id|
+          ids = uniq_ids.map do |id|
             if column_type == :integer
               id.to_i
             elsif column_type == :float