3 files changed, 42 insertions, 3 deletions
diff --git a/activemodel/CHANGELOG.md b/activemodel/CHANGELOG.md
index d98df4cb91..7dfc76ea8f 100644
--- a/activemodel/CHANGELOG.md
+++ b/activemodel/CHANGELOG.md
@@ -1,5 +1,10 @@
 ## Rails 3.2.10 (unreleased) ##
 
+*   Fix `validates_presence_of` with `:allow_nil` or `:allow_blank` options.
+    Fixes #8621.
+
+    *Colin Kelley and Rafael Mendonça França*
+
 *   Specify type of singular association during serialization *Steve Klabnik*
 
 
diff --git a/activemodel/lib/active_model/validations/presence.rb b/activemodel/lib/active_model/validations/presence.rb
index efd1372a6b..20a57e3c59 100644
--- a/activemodel/lib/active_model/validations/presence.rb
+++ b/activemodel/lib/active_model/validations/presence.rb
@@ -4,8 +4,8 @@ module ActiveModel
   # == Active Model Presence Validator
   module Validations
     class PresenceValidator < EachValidator
-      def validate(record)
-        record.errors.add_on_blank(attributes, options)
+      def validate_each(record, attr_name, value)
+        record.errors.add(attr_name, :blank, options) if value.blank?
       end
     end
 
@@ -39,7 +39,7 @@ module ActiveModel
       #   if the validation should not occur (e.g. <tt>:unless => :skip_validation</tt>,
       #   or <tt>:unless => Proc.new { |user| user.signup_step <= 2 }</tt>). The method,
       #   proc or string should return or evaluate to a true or false value.
-      # * <tt>:strict</tt> - Specifies whether validation should be strict. 
+      # * <tt>:strict</tt> - Specifies whether validation should be strict.
       #   See <tt>ActiveModel::Validation#validates!</tt> for more information.
       def validates_presence_of(*attr_names)
         validates_with PresenceValidator, _merge_attributes(attr_names)
diff --git a/activemodel/test/cases/validations/presence_validation_test.rb b/activemodel/test/cases/validations/presence_validation_test.rb
index 510c13a7c3..fbb008f9ff 100644
--- a/activemodel/test/cases/validations/presence_validation_test.rb
+++ b/activemodel/test/cases/validations/presence_validation_test.rb
@@ -70,4 +70,38 @@ class PresenceValidationTest < ActiveModel::TestCase
     p[:karma] = "Cold"
     assert p.valid?
   end
+
+  def test_validates_presence_of_with_allow_nil_option
+    Topic.validates_presence_of(:title, :allow_nil => true)
+
+    t = Topic.new(:title => "something")
+    assert t.valid?
+
+    t.title = ""
+    assert t.invalid?
+    assert_equal ["can't be blank"], t.errors[:title]
+
+    t.title = "  "
+    assert t.invalid?
+    assert_equal ["can't be blank"], t.errors[:title]
+
+    t.title = nil
+    assert t.valid?
+  end
+
+  def test_validates_presence_of_with_allow_blank_option
+    Topic.validates_presence_of(:title, :allow_blank => true)
+
+    t = Topic.new(:title => "something")
+    assert t.valid?
+
+    t.title = ""
+    assert t.valid?
+
+    t.title = "  "
+    assert t.valid?
+
+    t.title = nil
+    assert t.valid?
+  end
 end