--- a/testing/web-platform/tests/resources/idlharness.js
+++ b/testing/web-platform/tests/resources/idlharness.js
@@ -1638,17 +1638,17 @@ IdlInterface.prototype.test_self = funct
                 aliases = [ rhs.value ];
             }
 
             // OK now actually check the aliases...
             var alias;
             if (exposed_in(exposure_set(this, this.exposureSet)) && 'document' in self) {
                 for (alias of aliases) {
                     assert_true(alias in self, alias + " should exist");
-                    assert_equals(self[alias], this.get_interface_object(), "self." + alias + " should be the same value as the interface object");
+                    assert_equals(self[alias], this.get_interface_object(), "self." + alias + " should be the same value as self." + this.get_qualified_name());
                     var desc = Object.getOwnPropertyDescriptor(self, alias);
                     assert_equals(desc.value, this.get_interface_object(), "wrong value in " + alias + " property descriptor");
                     assert_true(desc.writable, alias + " should be writable");
                     assert_false(desc.enumerable, alias + " should not be enumerable");
                     assert_true(desc.configurable, alias + " should be configurable");
                     assert_false('get' in desc, alias + " should not have a getter");
                     assert_false('set' in desc, alias + " should not have a setter");
                 }