diff --git a/env/rust.scm b/env/rust.scm
index f6b55f2..a268188 100644
--- a/env/rust.scm
+++ b/env/rust.scm
@@ -180,13 +180,14 @@ function."
 
   (let* ((target (string-append (@@ (env) %env-directory)
                                 "/" (symbol->string target-sym)))
-         ;; TODO should actually detect if overlay is mounted not that the
-         ;; directory exists.
-         (mnt (mount-environment env #:tag onto #:target target))
+         (mnt (if (environment-mounted? env)
+                  (or (environment->overlay-mount-maybe env)
+                      (throw 'wrong-mount?))
+                  (mount-environment env #:tag onto #:target target)))
          (mappings (append (map (remap #f) expose)
                            (map (remap #t) share))))
     (exec-in-rustup-environment '("./.cargo/bin/rust-analyzer")
-                                #:home mnt
+                                #:home (overlay-mount-merged mnt)
                                 #:mappings mappings)
     (sync)
     (system* "umount" target)