diff -up cups-1.3.7/backend/serial.c.str3649 cups-1.3.7/backend/serial.c
--- cups-1.3.7/backend/serial.c.str3649	2011-09-14 17:29:54.000000000 +0200
+++ cups-1.3.7/backend/serial.c	2011-09-14 17:30:29.000000000 +0200
@@ -499,7 +499,7 @@ main(int  argc,				/* I - Number of comm
   * stdin (otherwise you can't cancel raw jobs...)
   */
 
-  if (print_fd != 0)
+  if (!print_fd)
   {
 #ifdef HAVE_SIGSET /* Use System V signals over POSIX to avoid bugs */
     sigset(SIGTERM, SIG_IGN);