diff --git a/.emacs.d/lisp/init-sly.el b/.emacs.d/lisp/init-sly.el
index a55a2408..311fa1c9 100644
--- a/.emacs.d/lisp/init-sly.el
+++ b/.emacs.d/lisp/init-sly.el
@@ -29,7 +29,8 @@
                                                                ad-hoc-args
                                                                command-args
                                                                &allow-other-keys)
-  "Wrapper over `ambrevar/guix-environment'."
+  "Like `ambrevar/guix-environment' but cache profile to speed up switch.
+`lisp-repl-core-dumper' is used to speed up SBCL startup."
   (let* ((load-mtime (when load
                        (file-attribute-modification-time (file-attributes load))))
          (root (or (cl-getf args :root)
@@ -51,17 +52,20 @@
                                                (list :ad-hoc-args ad-hoc-args)
                                                (list :command-args command-args)
                                                args)))
-    `(("bash" "-c" ,(concat
-                     (format "source '%s/etc/profile'" root)
-                     " && LISP_REPL_CORE_PATH=" cache
-                     " lisp-repl-core-dumper sbcl")))))
+    `((,@(unless (not (eq nil (cl-getf args :pure?)))
+           '("env" "-i"))
+       ,(executable-find "bash") "--norc" "--noprofile" "-c"
+       ,(concat
+         (format "source '%s/etc/profile'" root)
+         " && LISP_REPL_CORE_PATH=" cache
+         " lisp-repl-core-dumper sbcl")))))
 
 (when (executable-find "lisp-repl-core-dumper")
   ;; Warning: ,restart-lisp does not take changes into account, the buffer must be re-created.
   (setq sly-lisp-implementations
         `((sbcl-ambrevar ("lisp-repl-core-dumper" "sbcl" "ambrevar"))
           (sbcl ("lisp-repl-core-dumper" "sbcl"))
-          (sbcl-nyxt ;; Faster, but not pure.  TODO: Can we purify it?  Run it in a container?  Try `env -i bash  --noprofile --norc...`.
+          (sbcl-nyxt ;; Faster, but not pure.  TODO: Run it in a container?
            ;; TODO: Add easy way to reload: must delete profile.  No need to delete dump if we use -f.
            (lambda ()
              (cl-flet ((ambrevar/prepare-sbcl-for-nyxt