diff --git a/drivers/tty/tty.c b/drivers/tty/tty.c
index 7af69877e..993cbbe3e 100644
--- a/drivers/tty/tty.c
+++ b/drivers/tty/tty.c
@@ -670,6 +670,9 @@ int safe;
 	if (isconsole(tp)) r = kbd_loadmap(m_ptr, safe);
 	break;
 
+    case TIOCSFON_OLD:
+	printf("TTY: old TIOCSFON ignored.\n");
+	break;
     case TIOCSFON:
 	/* Load a font into an EGA or VGA card (hs@hck.hr) */
 	if (isconsole(tp)) r = con_loadfont(m_ptr);
diff --git a/include/minix/ioctl.h b/include/minix/ioctl.h
index 88113039f..6f1bf0193 100755
--- a/include/minix/ioctl.h
+++ b/include/minix/ioctl.h
@@ -16,12 +16,18 @@
  * of the parameter in the high-order word. The 3 high bits of the high-
  * order word are used to encode the in/out/void status of the parameter.
  */
-#define _IOCPARM_MASK	0x1FFF
-#define _IOC_VOID	0x20000000
-#define _IOCTYPE_MASK	0xFFFF
-#define _IOC_IN		0x40000000
-#define _IOC_OUT	0x80000000
-#define _IOC_INOUT	(_IOC_IN | _IOC_OUT)
+#define _IOCPARM_MASK		0x0FFF
+#define _IOCPARM_MASK_BIG	0x0FFFFF
+#define _IOC_VOID		0x20000000
+#define _IOCTYPE_MASK		0xFFFF
+#define _IOC_IN			0x40000000
+#define _IOC_OUT		0x80000000
+#define _IOC_INOUT		(_IOC_IN | _IOC_OUT)
+
+/* Flag indicating ioctl format with only one type field, and more bits
+ * for the size field (using mask _IOCPARM_MASK_BIG).
+ */
+#define _IOC_BIG		0x10000000
 
 #define _IO(x,y)	((x << 8) | y | _IOC_VOID)
 #define _IOR(x,y,t)	((x << 8) | y | ((sizeof(t) & _IOCPARM_MASK) << 16) |\
@@ -31,11 +37,22 @@
 #define _IORW(x,y,t)	((x << 8) | y | ((sizeof(t) & _IOCPARM_MASK) << 16) |\
 				_IOC_INOUT)
 
+#define _IOW_BIG(y,t)  (y | ((sizeof(t) & _IOCPARM_MASK_BIG) << 8) \
+	| _IOC_IN | _IOC_BIG)
+#define _IOR_BIG(y,t)  (y | ((sizeof(t) & _IOCPARM_MASK_BIG) << 8) \
+	| _IOC_OUT | _IOC_BIG)
+#define _IORW_BIG(y,t) (y | ((sizeof(t) & _IOCPARM_MASK_BIG) << 8) \
+	| _IOC_INOUT | _IOC_BIG)
+
 /* Decode an ioctl call. */
-#define _MINIX_IOCTL_SIZE(i)   (((i) >> 16) & _IOCPARM_MASK)
-#define _MINIX_IOCTL_IOR(i)    ((i) & _IOC_OUT)
-#define _MINIX_IOCTL_IORW(i)   ((i) & _IOC_INOUT)
-#define _MINIX_IOCTL_IOW(i)    ((i) & _IOC_IN)
+#define _MINIX_IOCTL_SIZE(i)		(((i) >> 16) & _IOCPARM_MASK)
+#define _MINIX_IOCTL_IOR(i)		((i) & _IOC_OUT)
+#define _MINIX_IOCTL_IORW(i)		((i) & _IOC_INOUT)
+#define _MINIX_IOCTL_IOW(i)		((i) & _IOC_IN)
+
+/* Recognize and decode size of a 'big' ioctl call. */
+#define _MINIX_IOCTL_BIG(i) 		((i) & _IOC_BIG)
+#define _MINIX_IOCTL_SIZE_BIG(i)	(((i) >> 8) & _IOCPARM_MASK_BIG)
 
 #else
 /* No fancy encoding on a 16-bit machine. */
diff --git a/include/sys/ioc_tty.h b/include/sys/ioc_tty.h
index e2f09d227..948a41e09 100755
--- a/include/sys/ioc_tty.h
+++ b/include/sys/ioc_tty.h
@@ -22,7 +22,8 @@
 #define	TIOCSWINSZ	_IOW('T', 17, struct winsize)
 #define	TIOCGPGRP	_IOW('T', 18, int)
 #define	TIOCSPGRP	_IOW('T', 19, int)
-#define TIOCSFON	_IOW('T', 20, u8_t [8192])
+#define TIOCSFON_OLD	_IOW('T', 20, u8_t [8192])
+#define TIOCSFON	_IOW_BIG(1, u8_t [8192])
 
 /* Legacy <sgtty.h> */
 #define TIOCGETP	_IOR('t',  1, struct sgttyb)
diff --git a/servers/fs/device.c b/servers/fs/device.c
index 3426cbc49..3db2a10d3 100644
--- a/servers/fs/device.c
+++ b/servers/fs/device.c
@@ -24,6 +24,7 @@
 #include <minix/com.h>
 #include <minix/endpoint.h>
 #include <minix/ioctl.h>
+#include <sys/ioc_tty.h>
 #include "file.h"
 #include "fproc.h"
 #include "inode.h"
@@ -239,7 +240,10 @@ off_t *pos;
 			*op = DEV_IOCTL_S;
 			if(_MINIX_IOCTL_IOR(m_in.REQUEST)) access |= CPF_WRITE;
 			if(_MINIX_IOCTL_IOW(m_in.REQUEST)) access |= CPF_READ;
-			size = _MINIX_IOCTL_SIZE(m_in.REQUEST);
+			if(_MINIX_IOCTL_BIG(m_in.REQUEST))
+				size = _MINIX_IOCTL_SIZE_BIG(m_in.REQUEST);
+			else
+				size = _MINIX_IOCTL_SIZE(m_in.REQUEST);
 
 			/* Do this even if no I/O happens with the ioctl, in
 			 * order to disambiguate requests with DEV_IOCTL_S.