diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 9d2c9d3b9c92c8595e4fc4e7d88a84f1dc4b05ef..06c8bceb30d65c2529e752770af79e6edc4b0869 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -188,7 +188,7 @@ def delete
     # and <tt>destroy</tt> returns +false+. See
     # ActiveRecord::Callbacks for further details.
     def destroy
-      raise ReadOnlyRecord if readonly?
+      raise ReadOnlyRecord, "#{self.class} is marked as readonly" if readonly?
       destroy_associations
       destroy_row if persisted?
       @destroyed = true
@@ -519,7 +519,7 @@ def relation_for_destroy
     end
 
     def create_or_update
-      raise ReadOnlyRecord if readonly?
+      raise ReadOnlyRecord, "#{self.class} is marked as readonly" if readonly?
       result = new_record? ? _create_record : _update_record
       result != false
     end
diff --git a/activerecord/test/cases/readonly_test.rb b/activerecord/test/cases/readonly_test.rb
index 2afd25c98985dbc005a7608ac4deb1f842d880f3..37d277eaa1538b22991812ed3850e690a2ccac68 100644
--- a/activerecord/test/cases/readonly_test.rb
+++ b/activerecord/test/cases/readonly_test.rb
@@ -22,9 +22,12 @@ def test_cant_save_readonly_record
       assert !dev.save
       dev.name = 'Forbidden.'
     end
-    assert_raise(ActiveRecord::ReadOnlyRecord) { dev.save  }
-    assert_raise(ActiveRecord::ReadOnlyRecord) { dev.save! }
-    assert_raise(ActiveRecord::ReadOnlyRecord) { dev.destroy }
+    e = assert_raise(ActiveRecord::ReadOnlyRecord) { dev.save  }
+    assert_equal "Developer is marked as readonly", e.message
+    e = assert_raise(ActiveRecord::ReadOnlyRecord) { dev.save! }
+    assert_equal "Developer is marked as readonly", e.message
+    e = assert_raise(ActiveRecord::ReadOnlyRecord) { dev.destroy }
+    assert_equal "Developer is marked as readonly", e.message
   end