diff --git a/mypy/test/testtypes.py b/mypy/test/testtypes.py
index 37007a01e..2f71b4428 100644
--- a/mypy/test/testtypes.py
+++ b/mypy/test/testtypes.py
@@ -59,6 +59,7 @@
 
 class TypesSuite(Suite):
     def setUp(self) -> None:
+        mypy.options._based = False
         self.x = UnboundType("X")  # Helpers
         self.y = UnboundType("Y")
         self.fx = TypeFixture()