diff --git a/Lib/unittest/loader.py b/Lib/unittest/loader.py
index 4e9e152..eea5c13 100644
--- a/Lib/unittest/loader.py
+++ b/Lib/unittest/loader.py
@@ -10,6 +10,7 @@
 
 from . import case, suite, util
 
+__unittest = True
 
 # what about .pyc or .pyo (etc)
 # we would need to avoid loading the same tests multiple times