diff --git a/activerecord/lib/active_record/enum.rb b/activerecord/lib/active_record/enum.rb
index efea9560eed3b67174044131c2d82b314bd3f790..6bfdf75a2dbecfad3ef3cc8a65e527f9b15a4fb7 100644
--- a/activerecord/lib/active_record/enum.rb
+++ b/activerecord/lib/active_record/enum.rb
@@ -42,7 +42,12 @@ def enum(definitions)
 
         _enum_methods_module.module_eval do
           # def direction=(value) self[:direction] = DIRECTION[value] end
-          define_method("#{name}=") { |value| self[name] = enum_values[value] }
+          define_method("#{name}=") { |value|
+            unless enum_values.has_key?(value)
+              raise ArgumentError, "'#{value}' is not a valid #{name}"
+            end
+            self[name] = enum_values[value]
+          }
 
           # def direction() DIRECTION.key self[:direction] end
           define_method(name) { enum_values.key self[name] }
diff --git a/activerecord/test/cases/enum_test.rb b/activerecord/test/cases/enum_test.rb
index bb9faccf1bdd5df6c22b1b48fea31c6ccbac3024..087db4c32c4e26c9c4decbcd8b549e5348c09ee3 100644
--- a/activerecord/test/cases/enum_test.rb
+++ b/activerecord/test/cases/enum_test.rb
@@ -40,4 +40,16 @@ class EnumTest < ActiveRecord::TestCase
     assert_equal "do publish work...", @book.published!
     assert @book.published?
   end
+
+  test "direct assignment" do
+    @book.status = :written
+    assert @book.written?
+  end
+
+  test "assign non existing value raises an error" do
+    e = assert_raises(ArgumentError) do
+      @book.status = :unknown
+    end
+    assert_equal "'unknown' is not a valid status", e.message
+  end
 end