diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index c5e8207f147da69c172ceb611b813a5644b576aa..856d872bcef29f727b16cf238a8b991f66b9a99a 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -759,6 +759,7 @@ def has_many(association_id, options = {}, &extension)
       # * <tt>:foreign_key</tt> - Specify the foreign key used for the association. By default this is guessed to be the name
       #   of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_one+ association will use "person_id"
       #   as the default <tt>:foreign_key</tt>.
+      # * <tt>:primary_key</tt> - Specify the method that returns the primary key used for the association. By default this is +id+.
       # * <tt>:include</tt> - Specify second-order associations that should be eager loaded when this object is loaded.
       # * <tt>:as</tt> - Specifies a polymorphic interface (See <tt>belongs_to</tt>).
       # * <tt>:select</tt> - By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if, for example, you want to do a join
@@ -1366,7 +1367,7 @@ def create_has_many_reflection(association_id, options, &extension)
 
         def create_has_one_reflection(association_id, options)
           options.assert_valid_keys(
-            :class_name, :foreign_key, :remote, :select, :conditions, :order, :include, :dependent, :counter_cache, :extend, :as, :readonly, :validate
+            :class_name, :foreign_key, :remote, :select, :conditions, :order, :include, :dependent, :counter_cache, :extend, :as, :readonly, :validate, :primary_key
           )
 
           create_reflection(:has_one, association_id, options, self)
diff --git a/activerecord/lib/active_record/associations/has_one_association.rb b/activerecord/lib/active_record/associations/has_one_association.rb
index 25a268e95cb0c8f063b378513497000dd5c6d5a3..fdc0fa52c9d3d7bf2deaede2c533761f564843d0 100755
--- a/activerecord/lib/active_record/associations/has_one_association.rb
+++ b/activerecord/lib/active_record/associations/has_one_association.rb
@@ -47,7 +47,16 @@ def replace(obj, dont_save = false)
           return (obj.nil? ? nil : self)
         end
       end
-            
+
+      protected
+        def owner_quoted_id
+          if @reflection.options[:primary_key]
+            quote_value(@owner.send(@reflection.options[:primary_key]))
+          else
+            @owner.quoted_id
+          end
+        end
+
       private
         def find_target
           @reflection.klass.find(:first, 
diff --git a/activerecord/test/cases/associations/has_one_associations_test.rb b/activerecord/test/cases/associations/has_one_associations_test.rb
index d3ca0cae414b53829cdbdcabc7971726f2e33384..99639849a5a60d37eb6888938a9c0d07b17ca327 100755
--- a/activerecord/test/cases/associations/has_one_associations_test.rb
+++ b/activerecord/test/cases/associations/has_one_associations_test.rb
@@ -29,6 +29,13 @@ def test_with_select
     assert_equal Firm.find(1, :include => :account_with_select).account_with_select.attributes.size, 2
   end
 
+  def test_finding_using_primary_key
+    firm = companies(:first_firm)
+    assert_equal Account.find_by_firm_id(firm.id), firm.account
+    firm.firm_id = companies(:rails_core).id
+    assert_equal accounts(:rails_core_account), firm.account_using_primary_key
+  end
+
   def test_can_marshal_has_one_association_with_nil_target
     firm = Firm.new
     assert_nothing_raised do
diff --git a/activerecord/test/cases/reflection_test.rb b/activerecord/test/cases/reflection_test.rb
index 0c57b79401b0c9fa712503af86ff42de8378769f..723062e3b8e9ceffc94fed239db087cb12a338fd 100644
--- a/activerecord/test/cases/reflection_test.rb
+++ b/activerecord/test/cases/reflection_test.rb
@@ -160,9 +160,9 @@ def test_association_reflection_in_modules
 
   def test_reflection_of_all_associations
     # FIXME these assertions bust a lot
-    assert_equal 22, Firm.reflect_on_all_associations.size
-    assert_equal 17, Firm.reflect_on_all_associations(:has_many).size
-    assert_equal 5, Firm.reflect_on_all_associations(:has_one).size
+    assert_equal 24, Firm.reflect_on_all_associations.size
+    assert_equal 18, Firm.reflect_on_all_associations(:has_many).size
+    assert_equal 6, Firm.reflect_on_all_associations(:has_one).size
     assert_equal 0, Firm.reflect_on_all_associations(:belongs_to).size
   end
 
diff --git a/activerecord/test/models/company.rb b/activerecord/test/models/company.rb
index c45a21b6a289c24fb6ab1068cc993232ed625cdb..e6aa810146e9cccf2210dc944aa11fca98c33f6c 100755
--- a/activerecord/test/models/company.rb
+++ b/activerecord/test/models/company.rb
@@ -53,6 +53,7 @@ class Firm < Company
   has_one :unvalidated_account, :foreign_key => "firm_id", :class_name => 'Account', :validate => false
   has_one :account_with_select, :foreign_key => "firm_id", :select => "id, firm_id", :class_name=>'Account'
   has_one :readonly_account, :foreign_key => "firm_id", :class_name => "Account", :readonly => true
+  has_one :account_using_primary_key, :primary_key => "firm_id", :class_name => "Account"
 end
 
 class DependentFirm < Company