3 files changed, 12 insertions, 0 deletions
diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 93935c0473..76e6ad93a7 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -169,9 +169,11 @@ module ActiveModel
     # If no +messsage+ is supplied, :invalid is assumed.
     # 
     # If +message+ is a Symbol, it will be translated, using the appropriate scope (see translate_error).
+    # If +message+ is a Proc, it will be called, allowing for things like Time.now to be used within an error
     def add(attribute, message = nil, options = {})
       message ||= :invalid
       message = generate_message(attribute, message, options) if message.is_a?(Symbol)
+      message = message.call if message.is_a?(Proc)
       self[attribute] << message
     end
 
diff --git a/activemodel/lib/active_model/validations/validates.rb b/activemodel/lib/active_model/validations/validates.rb
index 4c82a993ae..90b244228a 100644
--- a/activemodel/lib/active_model/validations/validates.rb
+++ b/activemodel/lib/active_model/validations/validates.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/hash/slice'
+
 module ActiveModel
   module Validations
     module ClassMethods
diff --git a/activemodel/test/cases/validations_test.rb b/activemodel/test/cases/validations_test.rb
index 38a2a716a7..eb100d1c35 100644
--- a/activemodel/test/cases/validations_test.rb
+++ b/activemodel/test/cases/validations_test.rb
@@ -212,4 +212,12 @@ class ValidationsTest < ActiveModel::TestCase
     all_errors = t.errors.to_a
     assert_deprecated { assert_equal all_errors, t.errors.each_full{|err| err} }
   end
+
+  def test_validation_with_message_as_proc
+    Topic.validates_presence_of(:title, :message => proc { "no blanks here".upcase })
+
+    t = Topic.new
+    assert !t.valid?
+    assert ["NO BLANKS HERE"], t.errors[:title]
+  end
 end