diff --git a/src/superio/winbond/w83627thf/w83627thf_early_serial.c b/src/superio/winbond/w83627thf/w83627thf_early_serial.c
index fb3598c102..325d14dd1f 100644
--- a/src/superio/winbond/w83627thf/w83627thf_early_serial.c
+++ b/src/superio/winbond/w83627thf/w83627thf_early_serial.c
@@ -1,11 +1,25 @@
 #include <arch/romcc_io.h>
 #include "w83627thf.h"
 
-
-static void w83627thf_enable_serial(device_t dev, unsigned iobase)
+static inline void pnp_enter_ext_func_mode(device_t dev)
 {
+	unsigned int port = dev >> 8;
+	outb(0x87, port);
+	outb(0x87, port);
+}
+
+static void pnp_exit_ext_func_mode(device_t dev)
+{
+	unsigned int port = dev >> 8;
+	outb(0xaa, port);
+}
+
+static void w83627thf_enable_serial(device_t dev, unsigned int iobase)
+{
+	pnp_enter_ext_func_mode(dev);
 	pnp_set_logical_device(dev);
 	pnp_set_enable(dev, 0);
 	pnp_set_iobase(dev, PNP_IDX_IO0, iobase);
 	pnp_set_enable(dev, 1);
+	pnp_exit_ext_func_mode(dev);
 }