Luckily, his spin doctors stepped in to help him out - by sending his secret strategy briefing to the media.
In a move that makes playing Lib Dem interview bingo even easier, somebody emailed 'Five things to remember' to political journalists attending the conference in Glasgow.
— Nick Sutton (@suttonnick) September 16, 2013
Top of the list is 'This conference sees the party in a confident mood', followed by the Lib Dems' 'proud achievements', and digs at Labour and the Tories.
Not everyone was convinced it was an accident, however:
Some pundits suggested a masterstroke to get the media to keep repeating the Lib Dems' key messages.
The party certainly seems to struggle to keep its private conversations out of the public gaze.
And last year Clegg retreated from a hastily-sent email branding gay marriage critics 'bigots'.