diff --git a/guix/build/emacs-build-system.scm b/guix/build/emacs-build-system.scm
index 8156757be..b77984742 100644
--- a/guix/build/emacs-build-system.scm
+++ b/guix/build/emacs-build-system.scm
@@ -116,22 +116,21 @@ store in '.el' files."
          ;; strings containing NULs.  Filter out such files.  TODO: Remove
          ;; this workaround when <https://bugs.gnu.org/30116> is fixed.
          (el-files (remove file-contains-nul-char?
-                           (find-files "." "\\.el$")))
-
-         (substitute-cmd (lambda ()
+                           (find-files (getcwd) "\\.el$"))))
+    (define (substitute-program-names)
       (substitute* el-files
         (("\"/bin/([^.]\\S*)\"" _ cmd-name)
          (let ((cmd (which cmd-name)))
            (unless cmd
-                                  (error
-                                   "patch-el-files: unable to locate " cmd-name))
-                                (string-append "\"" cmd "\"")))))))
+             (error "patch-el-files: unable to locate " cmd-name))
+           (string-append "\"" cmd "\"")))))
+
     (with-directory-excursion el-dir
-      ;; Some old '.el' files (e.g., tex-buf.el in AUCTeX) are still encoded
-      ;; with the "ISO-8859-1" locale.
-      (unless (false-if-exception (substitute-cmd))
+      ;; Some old '.el' files (e.g., tex-buf.el in AUCTeX) are still
+      ;; ISO-8859-1-encoded.
+      (unless (false-if-exception (substitute-program-names))
         (with-fluids ((%default-port-encoding "ISO-8859-1"))
-          (substitute-cmd))))
+          (substitute-program-names))))
     #t))
 
 (define* (install #:key outputs