--- libgfortran/io/file_pos.c.save	2018-07-03 22:48:42.485018736 +0000
+++ libgfortran/io/file_pos.c	2018-07-04 07:51:43.494582145 +0000
@@ -511,7 +511,8 @@ st_flush (st_parameter_filepos *fpp)
       else
 	{
 	  needs_unlock = true;
-	  LOCK (&u->au->io_lock);
+	  if (u->au)
+	    LOCK (&u->au->io_lock);
 	}
 
       /* Make sure format buffer is flushed.  */