diff --git a/.appveyor.yml b/.appveyor.yml
index f202dc2..28dc6ec 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -46,6 +46,7 @@ environment:
   # common variables
   SETUP_PATH: .:.ci
   SET: test01
+  BASE: 3.15
 
   matrix:
   - CC: vs2019