diff --git a/app/models/member_role.rb b/app/models/member_role.rb
index d65e7b6..99b9396 100644
--- a/app/models/member_role.rb
+++ b/app/models/member_role.rb
@@ -72,9 +72,6 @@ class MemberRole < ActiveRecord::Base
   end
 
   def remove_inherited_roles
-    MemberRole.where(:inherited_from => id).group_by(&:member).
-        each do |member, member_roles|
-      member_roles.each(&:destroy)
-    end
+    MemberRole.where(:inherited_from => id).destroy_all
   end
 end
diff --git a/app/models/project.rb b/app/models/project.rb
index c35a867..e751c4b 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -844,7 +844,7 @@ class Project < ActiveRecord::Base
   end
 
   def remove_inherited_member_roles
-    member_roles = memberships.map(&:member_roles).flatten
+    member_roles = MemberRole.where(:member_id => membership_ids).to_a
     member_role_ids = member_roles.map(&:id)
     member_roles.each do |member_role|
       if member_role.inherited_from && !member_role_ids.include?(member_role.inherited_from)
diff --git a/db/migrate/20161002133421_add_index_on_member_roles_inherited_from.rb b/db/migrate/20161002133421_add_index_on_member_roles_inherited_from.rb
new file mode 100644
index 0000000..2a06a9e
--- /dev/null
+++ b/db/migrate/20161002133421_add_index_on_member_roles_inherited_from.rb
@@ -0,0 +1,5 @@
+class AddIndexOnMemberRolesInheritedFrom < ActiveRecord::Migration
+  def change
+    add_index :member_roles, :inherited_from
+  end
+end