That Meryl Streep can sing. Look at Postcards from the Edge, Mamma Mia, Into the Woods, and more.
And only a really good singer can sing as badly as she does in this charming if conventional biopic of the New York socialite who will forever be the worst singer to give a recital at Carnegie Hall.
Jenkins' story has inspired several plays, notably the West End hit Glorious!, and now this affectionate film portrait that is kept afloat by Streep's captivatingly addled performance.
Jenkins was a wealthy widow and generous patron of Manhattan musical culture, who decided at mid-life to fix her own star in its firmament. She was undaunted by her lack of talent, apparently because she was unaware of it.
She performed mostly invitation-only recitals in private salons for audiences whose fawning adoration was entirely mercenary.
Meanwhile, she was protected from the depredations of critics who would ultimately write lines such as "she can sing anything but notes" because her husband, agent and champion St Clair Bayfield, paid the hacks to lie or stay away.
But the disastrous Carnegie Hall debut at 76, in a public recital she paid to stage, changed everything. Both the true story and the film's version of it are a savoury blend of farce and pathos.
Grant's warm and wonderful performance foregrounds Bayfield's devotion while rather skating over his motives.
But the leading man is really Cosme McMoon (Helberg, from The Big Bang Theory), the benighted pianist engaged to accompany her. Watching his delight at the generous stipend curdle to horror as he realises the damage his reputation is sustaining, is one of the film's real pleasures.
What's in fatally short supply, though, is the emotional texture that can make Florence more than a figure of fun. There are glimpses of it notably during a revealing doctor's visit but the narrative is really just a chronological flat line and the film never really achieves an emotional or dramatic arc.
In a standout scene, McMoon and Jenkins play a Chopin Prelude in an impromptu duet in the pianist's shabby apartment.
For a moment, both are transported and the film looks like it will fly.
It's a moment gone too soon, though, and what might have been a remarkable film returns to being just a quite good one.
Review: Florence Foster Jenkins
Meryl Streep, Hugh Grant, Simon Helberg, Rebecca Ferguson, Nina Arianda, David Haig
110 mins Rating: PG (coarse language)
Charming with moments of magic