diff --git a/activerecord/CHANGELOG b/activerecord/CHANGELOG
index ea4e2edcae..4c58664a19 100644
--- a/activerecord/CHANGELOG
+++ b/activerecord/CHANGELOG
@@ -1,5 +1,13 @@
 *Rails 3.1.0 (unreleased)*
 
+* Deprecated the AssociationCollection constant. CollectionProxy is now the appropriate constant
+  to use, though be warned that this is not really a public API.
+
+  This should solve upgrade problems with the will_paginate plugin (and perhaps others). Thanks
+  Paul Battley for reporting.
+
+  [Jon Leighton]
+
 * ActiveRecord::MacroReflection::AssociationReflection#build_record has a new method signature.
 
   Before: def build_association(*options)
diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index d67475053e..ebc6b3efb0 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -1,5 +1,12 @@
+require 'active_support/deprecation'
+
 module ActiveRecord
   module Associations
+    AssociationCollection = ActiveSupport::Deprecation::DeprecatedConstantProxy.new(
+      'ActiveRecord::Associations::AssociationCollection',
+      'ActiveRecord::Associations::CollectionProxy'
+    )
+
     # Association proxies in Active Record are middlemen between the object that
     # holds the association, known as the <tt>@owner</tt>, and the actual associated
     # object, known as the <tt>@target</tt>. The kind of association any proxy is
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 8b7d2e4276..380ef57214 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -1599,4 +1599,23 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
       undef_method :old_build_association
     end
   end
+
+  def test_AssociationCollection_deprecated
+    assert_deprecated do
+      ActiveRecord::Associations::AssociationCollection.class_eval do
+        def foo
+          "bar"
+        end
+      end
+    end
+
+    author = Author.new
+    assert_equal "bar", author.posts.foo
+  ensure
+    ActiveSupport::Deprecation.silence do
+      ActiveRecord::Associations::AssociationCollection.class_eval do
+        undef_method :foo
+      end
+    end
+  end
 end