2 files changed, 12 insertions, 1 deletions
diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
index a7801963e8..e613d157aa 100644
--- a/activerecord/lib/active_record/inheritance.rb
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -203,7 +203,7 @@ module ActiveRecord
 
           if subclass.name != self.name
             unless descendants.include?(subclass)
-              raise ActiveRecord::SubclassNotFound.new("Invalid single-table inheritance type: #{subclass_name} is not a subclass of #{name}")
+              raise ActiveRecord::SubclassNotFound.new("Invalid single-table inheritance type: #{subclass.name} is not a subclass of #{name}")
             end
 
             subclass
diff --git a/activerecord/test/cases/inheritance_test.rb b/activerecord/test/cases/inheritance_test.rb
index 0286c85939..f67d85603a 100644
--- a/activerecord/test/cases/inheritance_test.rb
+++ b/activerecord/test/cases/inheritance_test.rb
@@ -213,6 +213,17 @@ class InheritanceTest < ActiveRecord::TestCase
     assert_raise(ActiveRecord::SubclassNotFound) { Company.new(:type => 'Account') }
   end
 
+  def test_new_with_unrelated_namespaced_type
+    without_store_full_sti_class do
+      e = assert_raises ActiveRecord::SubclassNotFound do
+        Namespaced::Company.new(type: 'Firm')
+      end
+
+      assert_equal "Invalid single-table inheritance type: Namespaced::Firm is not a subclass of Namespaced::Company", e.message
+    end
+  end
+
+
   def test_new_with_complex_inheritance
     assert_nothing_raised { Client.new(type: 'VerySpecialClient') }
   end