Change drawer icon back to back arrow

I'm using the new `DrawerLayout` to have side navigation. I'm using the drawer icon (the 'hamburger') like this: ``` @Override protected void onStart() { super.onStart(); mDrawerLayout = (DrawerLayout) findViewById(R.id.activity_main_drawerlayout); mDrawerToggle = new ActionBarDrawerToggle( this, mDrawerLayout, R.drawable.ic_navigation_drawer, R.string.app_name, R.string.app_name); mDrawerLayout.setDrawerListener(mDrawerToggle); getActionBar().setDisplayHomeAsUpEnabled(true); getActionBar().setHomeButtonEnabled(true); } ``` However, when I add a `Fragment` to the backstack, I want to display the back arrow again, so the user can navigate back to "home", and only then open the app drawer. How can I reset the drawer icon to the back icon? The arrow I want: