diff --git a/core/cubes/proof.el b/core/cubes/proof.el
index 1ca110f..8fe9b24 100644
--- a/core/cubes/proof.el
+++ b/core/cubes/proof.el
@@ -29,7 +29,7 @@
 (defcube fg42/proof-general-cube
   "Integrate Proof General with Fg42"
   :title "Proof General cube"
-  :flag-default t
+  :flag-default nil
   :flag proof-general
 
   (fpkg/use proof-general)