diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 003c94a409..5e3cf510b0 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -84,6 +84,11 @@ module ActiveModel
       messages.clear
     end
 
+    # Do the error messages include an error with key +error+?
+    def include?(error)
+      messages.include? error
+    end
+
     # Get messages for +key+
     def get(key)
       messages[key]
diff --git a/activemodel/test/cases/errors_test.rb b/activemodel/test/cases/errors_test.rb
index 8cb8f7ba44..a24cac40ad 100644
--- a/activemodel/test/cases/errors_test.rb
+++ b/activemodel/test/cases/errors_test.rb
@@ -27,6 +27,12 @@ class ErrorsTest < ActiveModel::TestCase
     end
   end
 
+  def test_include?
+    errors = ActiveModel::Errors.new(self)
+    errors[:foo] = 'omg'
+    assert errors.include?(:foo), 'errors should include :foo'
+  end
+
   test "should return true if no errors" do
     person = Person.new
     person.errors[:foo]