diff --git a/nix/default.nix b/nix/default.nix
index b96f2616ce5edd84b0aee4adeb956a8f6e90b6bf..891f96a366e7aceec214833d75f646a4b71ff08a 100644
--- a/nix/default.nix
+++ b/nix/default.nix
@@ -17,4 +17,8 @@ plugins.helpers.simple_plugin
      deps = [ unstablePckgs.llvmPackages_9.clang-unwrapped unstablePckgs.llvm_9 pkgs.gnused ];
      opamPackages = [ "camlp5" ];
      configure_options = "-with-clang-includedir=${unstablePckgs.llvmPackages_9.clang-unwrapped}";
+     preFramaCTests = ''
+       echo Configuring Why3 for frama-clang.
+       why3 config --full-config
+     '';
    }