diff --git a/pkgs/applications/editors/emacs/build-support/elpa2nix.el b/pkgs/applications/editors/emacs/build-support/elpa2nix.el
index b0b4ecedc360..97cf2fd58a06 100644
--- a/pkgs/applications/editors/emacs/build-support/elpa2nix.el
+++ b/pkgs/applications/editors/emacs/build-support/elpa2nix.el
@@ -34,9 +34,10 @@ The file can either be a tar file or an Emacs Lisp file."
 
 (let ((flag (getenv "turnCompilationWarningToError")))
   (when (and flag
-             (not (string-empty-p flag)))
+             ;; we do not use `string-empty-p' because it requires subr-x in Emacs <= 26
+             (not (string= flag "")))
     (setq byte-compile-error-on-warn t)))
 
 (let ((flag (getenv "ignoreCompilationError")))
-  (when (string-empty-p flag)
+  (when (string= flag "")
     (setq byte-compile-debug t)))