diff --git a/plugins/stoa/lib/ext/person.rb b/plugins/stoa/lib/ext/person.rb
index 514696b..d8aacb2 100644
--- a/plugins/stoa/lib/ext/person.rb
+++ b/plugins/stoa/lib/ext/person.rb
@@ -6,7 +6,7 @@ class Person
   validate :usp_id_or_invitation, :if => lambda { |person| person.environment && person.environment.plugin_enabled?(StoaPlugin)}
 
   def usp_id_or_invitation
-    if usp_id.blank? && (invitation_code.blank? || !Task.find(:first, :conditions => {:code => invitation_code}))
+    if usp_id.blank? && (invitation_code.blank? || !Task.pending.find(:first, :conditions => {:code => invitation_code}))
       errors.add(:usp_id, "can't register without usp_id or invitation")
     end
   end
diff --git a/plugins/stoa/test/unit/person.rb b/plugins/stoa/test/unit/person.rb
index 416cc0e..a395e08 100644
--- a/plugins/stoa/test/unit/person.rb
+++ b/plugins/stoa/test/unit/person.rb
@@ -2,6 +2,13 @@ require File.dirname(__FILE__) + '/../../../../test/test_helper'
 
 class StoaPlugin::Person < ActiveSupport::TestCase
 
+  def setup
+    @environment = Environment.default
+    @environment.enable_plugin(StoaPlugin)
+  end
+
+  attr_reader :environment
+
   should 'validates uniqueness of usp_id' do
     usp_id = 87654321
     fast_create(Person, :usp_id => usp_id)
@@ -12,8 +19,6 @@ class StoaPlugin::Person < ActiveSupport::TestCase
   end
 
   should 'allow nil usp_id only if person has an invitation_code' do
-    environment = Environment.default
-    environment.enable_plugin(StoaPlugin)
     person = Person.new(:environment => environment)
     person.valid?
     assert person.errors.invalid?(:usp_id)
@@ -34,5 +39,14 @@ class StoaPlugin::Person < ActiveSupport::TestCase
     assert !person.errors.invalid?(:usp_id)
   end
 
+  should 'not allow person register with a finished task' do
+    t = Task.create!(:code => 87654321)
+    t.finish
+    person = Person.new(:environment => environment, :invitation_code => 87654321)
+    person.valid?
+
+    assert person.errors.invalid?(:usp_id)
+  end
+
 end
 
--
libgit2 0.21.2