diff --git a/nix/default.nix b/nix/default.nix
index 8f882bd297bb195263019f584e91bb4954aaa4da..f7491f9276eeb85d7dafb21b1c7505d1df5bfe00 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
      '';
    }