rails issue #3923

gistfile1.diff

diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
index ba882be..b72aaa2 100644
--- a/activerecord/lib/active_record/relation/spawn_methods.rb
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -34,7 +34,7 @@ module ActiveRecord
       unless @where_values.empty?
         # Remove duplicates, last one wins.
         seen = Hash.new { |h,table| h[table] = {} }
-        merged_wheres = merged_wheres.reverse.reject { |w|
+        merged_wheres = merged_wheres.uniq.reverse.reject { |w|
           nuke = false
           if w.respond_to?(:operator) && w.operator == :==
             name              = w.left.name
diff --git a/activerecord/test/cases/named_scope_test.rb b/activerecord/test/cases/named_scope_test.rb
index 4a09a87..c0c22be 100644
--- a/activerecord/test/cases/named_scope_test.rb
+++ b/activerecord/test/cases/named_scope_test.rb
@@ -337,6 +337,11 @@ class NamedScopeTest < ActiveRecord::TestCase
     end
   end
 
+  def test_should_not_duplicates_where_values
+    where_values = Topic.where("1=1").foo.where_values
+    assert_equal ["1=1"], where_values
+  end
+
   def test_chaining_with_duplicate_joins
     join = "INNER JOIN comments ON comments.post_id = posts.id"
     post = Post.find(1)
diff --git a/activerecord/test/models/topic.rb b/activerecord/test/models/topic.rb
index fe424e6..a6657e2 100644
--- a/activerecord/test/models/topic.rb
+++ b/activerecord/test/models/topic.rb
@@ -8,6 +8,8 @@ class Topic < ActiveRecord::Base
   scope :approved, :conditions => {:approved => true}
   scope :rejected, :conditions => {:approved => false}
 
+  scope :foo, proc { scoped }
+
   scope :by_lifo, :conditions => {:author_name => 'lifo'}
 
   scope :approved_as_hash_condition, :conditions => {:topics => {:approved => true}}