diff --git a/configs/xtrs/src/xtr_serial.c b/configs/xtrs/src/xtr_serial.c
index d4212835243..7aa99a87da6 100644
--- a/configs/xtrs/src/xtr_serial.c
+++ b/configs/xtrs/src/xtr_serial.c
@@ -132,6 +132,9 @@ static const struct uart_ops_s g_uart_ops =
   up_receive,               /* receive */
   up_rxint,                 /* rxint */
   up_rxavailable,           /* rxavailable */
+#ifdef CONFIG_SERIAL_IFLOWCONTROL
+  NULL,                     /* rxflowcontrol */
+#endif
   up_send,                  /* send */
   up_txint,                 /* txint */
   up_txready,               /* txready */
diff --git a/configs/z80sim/src/z80_serial.c b/configs/z80sim/src/z80_serial.c
index 4df2e06725c..7a13ea69b29 100644
--- a/configs/z80sim/src/z80_serial.c
+++ b/configs/z80sim/src/z80_serial.c
@@ -97,6 +97,9 @@ static const struct uart_ops_s g_uart_ops =
   up_receive,               /* receive */
   up_rxint,                 /* rxint */
   up_rxavailable,           /* rxavailable */
+#ifdef CONFIG_SERIAL_IFLOWCONTROL
+  NULL,                     /* rxflowcontrol */
+#endif
   up_send,                  /* send */
   up_txint,                 /* txint */
   up_txready,               /* txready */