diff --git a/lisp/progmodes/prolog.el b/lisp/progmodes/prolog.el
index 9ee405b..fffa7cc 100644
--- a/lisp/progmodes/prolog.el
+++ b/lisp/progmodes/prolog.el
@@ -1374,8 +1374,10 @@ prolog-ensure-process
       ()
     (with-current-buffer (get-buffer-create "*prolog*")
       (prolog-inferior-mode)
-      (apply 'make-comint-in-buffer "prolog" (current-buffer)
-             (prolog-program-name) nil (prolog-program-switches))
+      (let ((process-environment
+             (cons "INFERIOR=yes" process-environment)))
+        (apply 'make-comint-in-buffer "prolog" (current-buffer)
+               (prolog-program-name) nil (prolog-program-switches)))
       (unless prolog-system
         ;; Setup auto-detection.
         (setq-local