Former French Prime Minister Manuel Valls was flour-bombed by a protester during a campaign in Strasbourg on Thursday.
The man was protesting against a French Parliamentary procedure known as "49.3", which would see unpopular bills forced through parliament.
"We do not forget the 49.3," he screamed at Mr Valls, who is the leading candidate in the Socialist presidential primary. "We don't forgive it."
Mr Valls has said he'd like to see the powers in the 49.3 clause limited to budget legislation only.
However, Mr Valls himself used the clause to force through controversial labour reforms this year while he was Prime Minister, upsetting fellow Socialists in the process.
The man was detained by police at the walkabout campaign, held in a Christmas market, where Mr Valls was discussing security measures in light of the Berlin terror attack.
"Very nice trip to #Strasbourg: a few grams of flour but pounds of smiles," Mr Valls tweeted on his official account later that day.
"There is nothing worse than a campaign where nothing happens. We even got a little bombed with gluten-free flour," Mr Valls added light-heartedly at their next campaign stop.