diff --git a/lib/application_checker.rb b/lib/application_checker.rb
index 967a91b..03aa788 100644
--- a/lib/application_checker.rb
+++ b/lib/application_checker.rb
@@ -112,6 +112,27 @@ module Rails
         end
       end
       
+      # Check for deprecated constants
+      def check_deprecated_constants
+        files = []
+        ["RAILS_ENV", "RAILS_ROOT", "RAILS_DEFAULT_LOGGER"].each do |v|
+          lines = grep_for(v, "app/")
+          files += extract_filenames(lines) || []
+          
+          lines = grep_for(v, "lib/")
+          files += extract_filenames(lines) || []
+        end
+        
+        unless files.empty?
+          alert(
+            "Deprecated constant(s)", 
+            "Constants like RAILS_ENV, RAILS_ROOT, and RAILS_DEFAULT_LOGGER are now deprecated.",
+            "http://litanyagainstfear.com/blog/2010/02/03/the-rails-module/",
+            files.uniq
+          )
+        end
+      end
+      
       # Check for old-style config.gem calls
       def check_gems
         lines = grep_for("config.gem ", "config/*.rb")
diff --git a/test/application_checker_test.rb b/test/application_checker_test.rb
index 3634477..caadc55 100644
--- a/test/application_checker_test.rb
+++ b/test/application_checker_test.rb
@@ -147,6 +147,20 @@ class ApplicationCheckerTest < ActiveSupport::TestCase
     assert !@checker.alerts.has_key?("Old router API")
   end
   
+  def test_check_deprecated_constants_in_app_code
+    make_file("app/controllers/", "thing_controller.rb", "class ThingController; THING = RAILS_ENV; end;")
+    @checker.check_deprecated_constants
+    
+    assert @checker.alerts.has_key?("Deprecated constant(s)")
+  end
+  
+  def test_check_deprecated_constants_in_lib
+    make_file("lib/", "extra_thing.rb", "class ExtraThing; THING = RAILS_ENV; end;")
+    @checker.check_deprecated_constants
+    
+    assert @checker.alerts.has_key?("Deprecated constant(s)")
+  end
+  
   def teardown
     clear_files