Black Sabbath rockers Geezer Butler and Tony Iommi have warned fans not to expect another new album from the heavy metal stars, because the success of their recent comeback release makes for a perfect "final chapter". Ozzy Osbourne's reunited group scored its first U.S. number one in June (13), when 13 raced to the top of the charts. The album also hit the top of global countdowns, and it recently topped rock bible Revolver's Best Albums of 2013 poll. But, although frontman Osbourne has revealed he is "open" to recording more new material with his bandmates, bassist Butler and guitarist Iommi aren't so keen. Butler tells Classic Rock magazine, "To me, it's been nicely rounded off now. If we did another album, it just wouldn't have the same vibe as far as I'm concerned. And, with this one doing so well, the next one would have to be number one everywhere too or people would see it as a failure." Iommi, who has been battling cancer since the start of 2012, adds, "Making 13 was such a great, memorable experience, so if that's the final chapter, we'd have to be happy. We've not spoken about (another album). I don't know if it would be the right thing to do. God knows what the expectations would be next time around... I'd probably have a heart attack worrying about it!''