diff --git a/lib/factory_girl/factory.rb b/lib/factory_girl/factory.rb
index f969fb4..66f1a9a 100644
--- a/lib/factory_girl/factory.rb
+++ b/lib/factory_girl/factory.rb
@@ -1,5 +1,8 @@
 class Factory
-
+  
+  class AttributeDefinitionError < RuntimeError
+  end
+  
   cattr_accessor :factories, :sequences #:nodoc:
   self.factories = {}
   self.sequences = {}
@@ -94,6 +97,13 @@ class Factory
   #     If no block is given, this value will be used for this attribute.
   def add_attribute (name, value = nil, &block)
     name = name.to_sym
+
+    if name.to_s =~ /=$/
+      raise AttributeDefinitionError, 
+        "factory_girl uses 'f.#{name.to_s.chop} #{value}' syntax " +
+        "rather than 'f.#{name} #{value}'" 
+    end
+    
     if block_given?
       unless value.nil?
         raise ArgumentError, "Both value and block given"
diff --git a/test/factory_test.rb b/test/factory_test.rb
index 64cad57..91a9eaf 100644
--- a/test/factory_test.rb
+++ b/test/factory_test.rb
@@ -52,6 +52,14 @@ class FactoryTest < Test::Unit::TestCase
     end
 
   end
+  
+  should "raise an error when defining a factory when using attribute setters" do
+    assert_raise Factory::AttributeDefinitionError do
+      Factory.define(:user) do |f|
+        f.name = 'test'
+      end
+    end
+  end
 
   context "defining a sequence" do