diff --git a/support/testing/infra/basetest.py b/support/testing/infra/basetest.py
index 1ae6232da8..4f020e8a93 100644
--- a/support/testing/infra/basetest.py
+++ b/support/testing/infra/basetest.py
@@ -24,8 +24,8 @@ MINIMAL_CONFIG = \
 
 class BRConfigTest(unittest.TestCase):
     """Test up to the configure stage."""
-    config = None
-    br2_external = list()
+    config: str
+    br2_external: list[str] = list()
     downloaddir = None
     outputdir = None
     logtofile = True