diff --git a/drivers/serial/ptmx.c b/drivers/serial/ptmx.c
index f38da9c93fd..ed699dc85df 100644
--- a/drivers/serial/ptmx.c
+++ b/drivers/serial/ptmx.c
@@ -206,12 +206,10 @@ static int ptmx_open(FAR struct file *filep)
   /* Open the master device:  /dev/ptyN, where N=minor */
 
   snprintf(devname, sizeof(devname), "/dev/pty%d", minor);
-  memcpy(&temp, filep, sizeof(temp));
-  ret = file_open(filep, devname, O_RDWR | O_CLOEXEC);
+  ret = file_open(&temp, devname, O_RDWR | O_CLOEXEC);
   DEBUGASSERT(ret >= 0);  /* file_open() should never fail */
-
-  /* Close the multiplexor device: /dev/ptmx */
-
+  ret = file_dup2(&temp, filep);
+  DEBUGASSERT(ret >= 0);  /* file_dup2() should never fail) */
   ret = file_close(&temp);
   DEBUGASSERT(ret >= 0);  /* file_close() should never fail */