diff --git a/activesupport/lib/active_support/deprecation.rb b/activesupport/lib/active_support/deprecation.rb
index 76db7b5a56..3c1ceafcff 100644
--- a/activesupport/lib/active_support/deprecation.rb
+++ b/activesupport/lib/active_support/deprecation.rb
@@ -143,7 +143,8 @@ module ActiveSupport
         end
     end
 
-    # Stand-in for @request, @attributes, etc.
+    # Stand-in for @request, @attributes, @params, etc which emits deprecation
+    # warnings on any method call (except #inspect).
     class DeprecatedInstanceVariableProxy
       instance_methods.each { |m| undef_method m unless m =~ /^__/ }
 
@@ -151,6 +152,12 @@ module ActiveSupport
         @instance, @method, @var = instance, method, var
       end
 
+      # Don't give a deprecation warning on inspect since test/unit and error
+      # logs rely on it for diagnostics.
+      def inspect
+        target.inspect
+      end
+
       private
         def method_missing(called, *args, &block)
           warn caller, called, args
diff --git a/activesupport/test/deprecation_test.rb b/activesupport/test/deprecation_test.rb
index 5699ef78d6..9eb9e9253a 100644
--- a/activesupport/test/deprecation_test.rb
+++ b/activesupport/test/deprecation_test.rb
@@ -79,6 +79,10 @@ class DeprecationTest < Test::Unit::TestCase
     assert_deprecated('@request.to_s') { assert_equal @dtc.request.to_s, @dtc.old_request.to_s }
   end
 
+  def test_deprecated_instance_variable_proxy_shouldnt_warn_on_inspect
+    assert_not_deprecated { assert_equal @dtc.request.inspect, @dtc.old_request.inspect }
+  end
+
   def test_assert_deprecation_without_match
     assert_deprecated do
       @dtc.partially