diff --git a/nix/default.nix b/nix/default.nix
index b2a37e5fe4e2f4c19f52a3f96617c8e6808ead35..310063e709b5a2d3cd2137d8a2792a30425b5549 100644
--- a/nix/default.nix
+++ b/nix/default.nix
@@ -19,6 +19,6 @@ plugins.helpers.simple_plugin
      preFramaCTests = ''
        echo CONFIGURING Why3 for Frama_Clang.
        export HOME=$(mktemp -d)
-       why3 config --full-config
+       why3 config --detect
      '';
    }