diff --git a/winsup/cygwin/fhandler_termios.cc b/winsup/cygwin/fhandler_termios.cc
index 012ecb356..b72f01f22 100644
--- a/winsup/cygwin/fhandler_termios.cc
+++ b/winsup/cygwin/fhandler_termios.cc
@@ -133,7 +133,8 @@ tty_min::kill_pgrp (int sig)
   siginfo_t si = {0};
   si.si_signo = sig;
   si.si_code = SI_KERNEL;
-  last_sig = sig;
+  if (sig > 0 && sig < _NSIG)
+    last_sig = sig;
 
   for (unsigned i = 0; i < pids.npids; i++)
     {