--- a/src/cw.c
+++ b/src/cw.c
@@ -1173,7 +1173,7 @@
   close(master);
   return(0);
  }
- if(isastream(slave)){
+ if(fcntl(slave,F_GETFD) < 0){
   if(ioctl(slave,I_PUSH,"ptem")<0||ioctl(slave,I_PUSH,"ldterm")<0){
    close(master);
    close(slave);
@@ -1211,7 +1211,7 @@
   close(master);
   return(0);
  }
- if(isastream(slave)){
+ if(fcntl(slave,F_GETFD) < 0){
   if(ioctl(slave,I_PUSH,"ptem")<0||ioctl(slave,I_PUSH,"ldterm")<0){
    close(master);
    close(slave);