diff -rupN readline-8.1/signals.c readline-8.1-new/signals.c
--- readline-8.1/signals.c	2020-08-06 22:30:02.000000000 +0200
+++ readline-8.1-new/signals.c	2021-01-09 10:58:27.861297748 +0100
@@ -266,8 +266,10 @@ _rl_handle_signal (int sig)
     case SIGQUIT:
 #endif
 
+#if defined (HAVE_POSIX_SIGNALS)
       if (block_sig)
 	sigprocmask (SIG_BLOCK, &set, &oset);
+#endif
 
       rl_echo_signal_char (sig);
       rl_cleanup_after_signal ();