diff --git a/winsup/cygwin/fhandler/process.cc b/winsup/cygwin/fhandler/process.cc
index a8c17f1b0..b0aef2ebe 100644
--- a/winsup/cygwin/fhandler/process.cc
+++ b/winsup/cygwin/fhandler/process.cc
@@ -1092,9 +1092,11 @@ format_process_stat (void *data, char *&destbuf)
   int nice = 0;
 /* ctty maj is 31:16, min is 15:0; tty_nr s/b maj 15:8, min 31:20, 7:0;
    maj is 31:16 >> 16 & fff << 8; min is 15:0 >> 8 & ff << 20 | & ff */
-  int tty_nr =    (((p->ctty >>  8) & 0xff)  << 20)
-		| (((p->ctty >> 16) & 0xfff) <<  8)
-		|   (p->ctty        & 0xff);
+  int tty_nr = 0;
+  if (p->ctty > 0)
+    tty_nr =   (((p->ctty >>  8) & 0xff)  << 20)
+	     | (((p->ctty >> 16) & 0xfff) <<  8)
+	     |   (p->ctty        & 0xff);
 
   if (p->process_state & PID_EXITED)
     strcpy (cmd, "<defunct>");