diff --git a/activerecord/lib/active_record/associations/association_collection.rb b/activerecord/lib/active_record/associations/association_collection.rb
index 3aef1b2..49eb0b0 100644
--- a/activerecord/lib/active_record/associations/association_collection.rb
+++ b/activerecord/lib/active_record/associations/association_collection.rb
@@ -166,7 +166,10 @@ module ActiveRecord
       # Otherwise, construct options and pass them with scope to the target class's +count+.
       def count(*args)
         if @reflection.options[:counter_sql]
-          @reflection.klass.count_by_sql(@counter_sql)
+          conditions = sanitize_sql(args.last.is_a?(Hash) ? args.last[:conditions] : nil)
+          sql = @counter_sql
+          sql << " AND (#{conditions})" unless conditions.blank?
+          @reflection.klass.count_by_sql(sql)
         else
           column_name, options = @reflection.klass.send(:construct_count_options_from_args, *args)
           if @reflection.options[:uniq]
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 30edf79..507e534 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -28,6 +28,10 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal 2, Firm.find(:first).clients.count
   end
 
+  def test_counting_with_conditional_counter_sql
+    assert_equal 1, Firm.find(:first).clients.count(:conditions => ['name = ?', 'Microsoft'])
+  end
+
   def test_counting
     assert_equal 2, Firm.find(:first).plain_clients.count
   end