diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index c4b74c6477..2c66ddb983 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Cache `CollectionAssociation#reader` proxies separately before and after
+    the owner has been saved so that the proxy is not cached without the
+    owner's id.
+
+    *Ben Woosley*
+
 *   `ActiveRecord::ReadOnlyRecord` now has a descriptive message.
 
     *Franky W.*
diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 4411e5ae62..93f611dd8d 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -33,7 +33,13 @@ module ActiveRecord
           reload
         end
 
-        @proxy ||= CollectionProxy.create(klass, self)
+        if owner.new_record?
+          # Cache the proxy separately before the owner has an id
+          # or else a post-save proxy will still lack the id
+          @new_record_proxy ||= CollectionProxy.create(klass, self)
+        else
+          @proxy ||= CollectionProxy.create(klass, self)
+        end
       end
 
       # Implements the writer method, e.g. foo.items= for Foo.has_many :items
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 1617e883ba..69f7bde4bc 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -413,6 +413,13 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal "Summit", Firm.all.merge!(:order => "id").first.clients_using_primary_key.first.name
   end
 
+  def test_update_all_on_association_accessed_before_save
+    firm = Firm.new(name: 'Firm')
+    firm.clients << Client.first
+    firm.save!
+    assert_equal firm.clients.count, firm.clients.update_all(description: 'Great!')
+  end
+
   def test_belongs_to_sanity
     c = Client.new
     assert_nil c.firm, "belongs_to failed sanity check on new object"