(compile-internal): Set EMACS=t in process-environment.

1 files changed, 4 insertions, 3 deletions

diff --git a/lisp/progmodes/compile.el b/lisp/progmodes/compile.el
index 7e326e9b62a..c3c6b48f1c8 100644
--- a/lisp/progmodes/compile.el
+++ b/lisp/progmodes/compile.el
@@ -383,9 +383,10 @@ Returns the compilation buffer created."
         (compilation-set-window-height outwin)
         ;; Start the compilation.
         (if (fboundp 'start-process)
-            (let ((proc (start-process-shell-command (downcase mode-name)
-                                                     outbuf
-                                                     command)))
+            (let* ((process-environment (cons "EMACS=t" process-environment))
+                   (proc (start-process-shell-command (downcase mode-name)
+                                                      outbuf
+                                                      command)))
               (set-process-sentinel proc 'compilation-sentinel)
               (set-process-filter proc 'compilation-filter)
               (set-marker (process-mark proc) (point) outbuf)