diff --git a/gnu/packages/simulation.scm b/gnu/packages/simulation.scm
index 3e65d1687..a5b661e34 100644
--- a/gnu/packages/simulation.scm
+++ b/gnu/packages/simulation.scm
@@ -84,8 +84,6 @@
      `(("gzip" ,gzip)
        ("gnuplot" ,gnuplot)
        ("openmpi" ,openmpi)))
-    ;; FIXME: Also separate tutorials (80MB) and src (60MB); maybe also doc
-    ;; (8MB)
     (outputs '("debug"                  ;~60MB
                "out"))
     (arguments
@@ -176,14 +174,14 @@
                          "lockDir=$HOME/.$WM_PROJECT/.wmake\n"))
                       #t))
                   (add-after 'build 'cleanup
-                    ;; Avoid unncessary, voluminous object and dep files
+                    ;; Avoid unncessary, voluminous object and dep files.
                     (lambda _
                       (delete-file-recursively
                        "platforms/linux64GccDPInt32Opt/src")
                       (delete-file-recursively
                        "platforms/linux64GccDPInt32OptSYSTEMOPENMPI")
-                      (zero?
-                       (system* "find" "-name" "*.o" "-delete"))))
+                      (for-each delete-file (find-files "." "\\.o$"))
+                      #t))
                   (replace 'install
                     (lambda _
                       ;; use 'OpenFOAM-version' convention