fix fireball-x/fireball#189
fix fireball-x/fireball#189

bright-sparks/fireball,pombredanne/fireball,bright-sparks/fireball,pombredanne/fireball,abhishekgahlot/fireball,takaaptech/fireball,takaaptech/fireball,pombredanne/fireball,bright-sparks/fireball,abhishekgahlot/fireball,takaaptech/fireball,abhishekgahlot/fireball