To a fault

I am trusting to a fault.

1710, Isaac Norris, Friendly Advice to the Inhabitants of Pensilvania, Andrew Bradford (Philadelphia), p. 2, He also had that good qualification, of a moderate expectation, almost to a fault.

These mosquitoes […] are feeble, insignificant in size, diffident to a fault.

Fitz-Roy's character was a singular one, with very many noble features: he was devoted to his duty, generous to a fault, bold, determined, and indomitably energetic.

Madam, I'm as gentle as a jellyfish, and peaceful to a fault.

Self-deprecating to a fault, he refuses any praise for his work.

Charles has been described by his biographer Catherine Mayer as “loyal to a fault. Sometimes to the point of fault,” but this was too much.