diff --git a/configs/z80sim/src/Makefile b/configs/z80sim/src/Makefile
index 2bedb8da15..6ab51ade33 100644
--- a/configs/z80sim/src/Makefile
+++ b/configs/z80sim/src/Makefile
@@ -38,7 +38,7 @@
 ASRCS =
 CSRCS = z80_irq.c z80_timerisr.c z80_lowputc.c
 
-ifneq ($(CONFIG_NFILE_DESCRIPTOR),0)
+ifneq ($(CONFIG_NFILE_DESCRIPTORS),0)
 CSRCS += z80_serial.c
 endif
 
diff --git a/libc/termios/Make.defs b/libc/termios/Make.defs
index 91a4c4a6b6..c3a44f4085 100644
--- a/libc/termios/Make.defs
+++ b/libc/termios/Make.defs
@@ -42,7 +42,7 @@ ifeq ($(CONFIG_SERIAL_TERMIOS),y)
 # Add the termios C files to the build
 
 CSRCS += lib_cfgetspeed.c lib_cfsetspeed.c lib_isatty.c lib_tcflush.c
-CSRCS += lib_tcgetattr.c lib_tcsetattr.c
+CSRCS += lib_tcflow.c lib_tcgetattr.c lib_tcsetattr.c
 
 # Add the termios directory to the build
 
diff --git a/libc/termios/lib_tcflow.c b/libc/termios/lib_tcflow.c
new file mode 100644
index 0000000000..1ac7a7a7b4
--- /dev/null
+++ b/libc/termios/lib_tcflow.c
@@ -0,0 +1,85 @@
+/****************************************************************************
+ * libc/termios/lib_tcflow.c
+ *
+ *   Copyright (C) 2017 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <sys/ioctl.h>
+
+#include <termios.h>
+#include <errno.h>
+
+#include <nuttx/serial/tioctl.h>
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: tcflow
+ *
+ * Descripton:
+ *   The tcflow() function will suspend or restart transmission or reception
+ *   of data on the object referred to by 'fd', depending on the value of
+ *   'action'.
+ *
+ * Input Parameters:
+ *  fd     - An open file descriptor associated with a terminal.
+ *  action - Describes the action to be performed:
+ *           TCOOFF  - Output will be suspended.
+ *           TCOON   - Suspended output will be restarted.
+ *           TCIOFF  - The system will transmit a STOP character, which is
+ *                     intended to cause the terminal device to stop
+ *                     transmitting data to the system.
+ *           TCION   - The system will transmit a START character, which is
+ *                     intended to cause the terminal device to start
+ *                     transmitting data to the system.
+ *
+ *   The default on the opening of a terminal file is that neither its input nor
+ *   its output are suspended.
+ *
+ * Returned Value:
+ *   Upon successful completion, 0 is returned. Otherwise, -1 is returned and
+ *   errno is set to indicate the nature of the error.
+ *
+ ****************************************************************************/
+
+int tcflow(int fd, int action)
+{
+  return ioctl(fd, TCXONC, (unsigned long)action);
+}