A donor who gave money to Comic Relief on Red Nose Day discovered that the funds were only taken from his bank account 10 weeks after he made the pledge.
Peter McHugh, from Putney in south-west London, said he gave £75 to the charity on 11 March and had forgotten about it until he received a bank statement showing a debit to 'Red Nose' on 23 May.
He said: "It is worrying, because it seems that Comic Relief is not making the best of the donation. It makes me wonder how much they could be losing."
McHugh was also concerned that some donors might face problems if money went out of their accounts unexpectedly.
A spokeswoman for Comic Relief said the charity had "not been aware of the problem". She declined to discuss the issue further, saying only that a letter had gone out to McHugh directly.