2 files changed, 15 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index cb17b6e483..a1c8bd6e50 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -55,6 +55,12 @@ module ActiveRecord
     end
   end
 
+  class HasManyThroughCantCountOnColumnForGroupedAssociation < ActiveRecordError #:nodoc:
+    def initialize(owner, reflection, column_name)
+      super("Cannot count on column '#{column_name}' for association '#{owner.class.name}##{reflection.name}' grouped by '#{reflection.options[:group]}'.")
+    end
+  end
+
   class EagerLoadPolymorphicError < ActiveRecordError #:nodoc:
     def initialize(reflection)
       super("Can not eagerly load the polymorphic association #{reflection.name.inspect}")
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index 1ca44d645c..96d0b73da2 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -124,6 +124,15 @@ module ActiveRecord
           column_name = "#{@reflection.quoted_table_name}.#{@reflection.klass.primary_key}" if column_name == :all
           options.merge!(:distinct => true) 
         end
+
+        if @reflection.options[:group]
+          unless column_name == :all
+            raise HasManyThroughCantCountOnColumnForGroupedAssociation.new(@owner, @reflection, column_name)
+          end
+          column_name = @reflection.options[:group]
+          options.merge!(:distinct => true)
+        end
+
         @reflection.klass.send(:with_scope, construct_scope) { @reflection.klass.count(column_name, options) } 
       end