diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index f40298e..2e96ce0 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1227,7 +1227,8 @@
  *	init_dev		-	initialise a tty device
  *	@driver: tty driver we are opening a device on
  *	@idx: device index
- *	@tty: returned tty structure
+ *	@ret_tty: returned tty structure
+ *	@first_ok: ok to open a new device (used by ptmx)
  *
  *	Prepare a tty device. This may not be a "new" clean device but
  *	could also be an active device. The pty drivers require special
@@ -1248,7 +1249,7 @@
  */
 
 static int init_dev(struct tty_driver *driver, int idx,
-	struct tty_struct **ret_tty)
+	struct tty_struct **ret_tty, int first_ok)
 {
 	struct tty_struct *tty, *o_tty;
 	struct ktermios *tp, **tp_loc, *o_tp, **o_tp_loc;
@@ -1279,6 +1280,11 @@
 	}
 	if (tty) goto fast_track;
 
+	if (driver->subtype == PTY_TYPE_MASTER &&
+		(driver->flags & TTY_DRIVER_DEVPTS_MEM) && !first_ok) {
+		retval = -EIO;
+		goto end_init;
+	}
 	/*
 	 * First time open is complex, especially for PTY devices.
 	 * This code guarantees that either everything succeeds and the
@@ -1413,7 +1419,7 @@
 
 	if (retval)
 		goto release_mem_out;
-	 goto success;
+	goto success;
 
 	/*
 	 * This fast open can be used if the tty is already open.
@@ -1795,7 +1801,7 @@
 }
 
 /**
- *	tty_open		-	open a tty device
+ *	__tty_open		-	open a tty device
  *	@inode: inode of device file
  *	@filp: file pointer to tty
  *
@@ -1874,7 +1880,7 @@
 		return -ENODEV;
 	}
 got_driver:
-	retval = init_dev(driver, index, &tty);
+	retval = init_dev(driver, index, &tty, 0);
 	mutex_unlock(&tty_mutex);
 	if (retval)
 		return retval;
@@ -1971,7 +1977,7 @@
 		return index;
 
 	mutex_lock(&tty_mutex);
-	retval = init_dev(ptm_driver, index, &tty);
+	retval = init_dev(ptm_driver, index, &tty, 1);
 	mutex_unlock(&tty_mutex);
 
 	if (retval)