By Eliza Berman
December 15, 2015

Tina Fey and Amy Poehler may play wildly different siblings in Sisters, out Dec. 18, but it’s screenwriter Paula Pell’s teenage diary that inspired their rapport. The movie, which revolves around a middle-aged rager Kate and Maura Ellis throw in their childhood home, is a role reversal from the Saturday Night Live alumnae’s 2008 comedy Baby Mama. Here, Fey plays the irresponsible, inconsistently employed older sister to Poehler’s overachieving, designated-driver little sis.

It’s a dynamic straight out of Pell’s adolescence, which found her firmly in the realm of the G-rated while her more sexually adventurous sister racked up diaries full of lurid tales. The adult Ellis sisters are in many ways the grown-up extensions of the young Pell sisters—though their last-hurrah party offers Poehler’s Maura the chance to compensate for the Saturday nights she spent as a teenager recalibrating the settings on her rock tumbler.

In this exclusive featurette, Pell—who became friends with Fey and Poehler when they worked together on SNL, where she has served as a writer for two decades—reminisces about the prudish past that inspired the movie. Meanwhile, Fey, Poehler and costars Dianne Wiest, John Leguizamo, Bobby Moynihan and Samantha Bee try to keep it together while reading from the diary in which she confided.

Write to Eliza Berman at eliza.berman@time.com.

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