diff --git a/compiler/main.lisp b/compiler/main.lisp
index eac347dca2ec5c84fe6331fa7d304b64cb960f41..544ccb04acd3a150d0b689a328ffa983d11e5d95 100644
--- a/compiler/main.lisp
+++ b/compiler/main.lisp
@@ -1127,9 +1127,9 @@
 	 (generate-comment (file-info)
 	   (let* ((name (pathname (source-info-stream file-info)))
 		  (proc (run-git name))
-		  comment)
-	     (if (and proc (zerop (process-exit-code proc))
-		      (setf comment (read-line (process-output proc) nil nil)))
+		  (comment (and proc (zerop (process-exit-code proc))
+				(read-line (process-output proc) nil nil))))
+	     (if comment
 		 (format nil "$Header: ~A ~A $"
 			 (enough-namestring name)
 			 comment)