diff --git a/actionpack/CHANGELOG b/actionpack/CHANGELOG
index 7ce2fb5c5b5269763e41c05fe51a47753407eae8..e6fabd27fc1a67590434f9e8ecfc11f0497b26d0 100644
--- a/actionpack/CHANGELOG
+++ b/actionpack/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* assert_response failures include the exception message.  #10688 [Seth Rasmussen]
+
 * All fragment cache keys are now by default prefixed with the "views/" namespace [DHH]
 
 * Moved the caching stores from ActionController::Caching::Fragments::* to ActiveSupport::Cache::*. If you're explicitly referring to a store, like ActionController::Caching::Fragments::MemoryStore, you need to update that reference with ActiveSupport::Cache::MemoryStore [DHH]
diff --git a/actionpack/lib/action_controller/assertions/response_assertions.rb b/actionpack/lib/action_controller/assertions/response_assertions.rb
index 42bd7fb3d21c96d6b56c28de76dcb5b84742a3b3..67dd3a57241840e2eb6ec3a73c399e336ecfac76 100644
--- a/actionpack/lib/action_controller/assertions/response_assertions.rb
+++ b/actionpack/lib/action_controller/assertions/response_assertions.rb
@@ -33,7 +33,11 @@ def assert_response(type, message = nil)
           elsif type.is_a?(Symbol) && @response.response_code == ActionController::StatusCodes::SYMBOL_TO_STATUS_CODE[type]
             assert_block("") { true } # to count the assertion
           else
-            assert_block(build_message(message, "Expected response to be a <?>, but was <?>", type, @response.response_code)) { false }
+            if @response.error?
+              assert_block(build_message(message, "Expected response to be a <?>, but was <?>\n<?>", type, @response.response_code, @response.template.instance_variable_get(:@exception).message)) { false }
+            else
+              assert_block(build_message(message, "Expected response to be a <?>, but was <?>", type, @response.response_code)) { false }
+            end
           end
         end
       end
diff --git a/actionpack/test/controller/action_pack_assertions_test.rb b/actionpack/test/controller/action_pack_assertions_test.rb
index 1eb9610d04af8d9e81b7749f55368a4a57eea2d1..b1006f82be5197e8acf9df3adb9a521a6da124b0 100644
--- a/actionpack/test/controller/action_pack_assertions_test.rb
+++ b/actionpack/test/controller/action_pack_assertions_test.rb
@@ -124,6 +124,15 @@ def full_messages; ['...stuff...']; end
   def rescue_action(e) raise; end
 end
 
+# Used to test that assert_response includes the exception message
+# in the failure message when an action raises and assert_response
+# is expecting something other than an error.
+class AssertResponseWithUnexpectedErrorController < ActionController::Base
+  def index
+    raise 'FAIL'
+  end
+end
+
 module Admin
   class InnerModuleController < ActionController::Base
     def index
@@ -465,6 +474,15 @@ def test_assert_valid_failing
     rescue Test::Unit::AssertionFailedError => e
     end
   end
+
+  def test_assert_response_uses_exception_message
+    @controller = AssertResponseWithUnexpectedErrorController.new
+    get :index
+    assert_response :success
+    flunk 'Expected non-success response'
+  rescue Test::Unit::AssertionFailedError => e
+    assert e.message.include?('FAIL')
+  end
 end
 
 class ActionPackHeaderTest < Test::Unit::TestCase