'Judy' costume designer Jany Temime had "technical problems" because of Judy Garland's spinal curvature.
Renee Zellweger - who portrays the late singer-and-actress in the new biopic - spent "hours and hours" with the wardrobe department because she wanted to look "right" as the starlet and her hunched posture made it hard to get the outfits to fit properly.
Jany told Britain's HELLO! magazine: "The dresses are very tight because Renee wanted to accentuate the S shape.
"Not because she was vain or wanted to look good, it's because she wanted it to look right. I've never seen anyone work so hard.
"But it gave me technical problems.
"She'd come in, we'd have the dress, she'd put it on and she was the glamorous star. Then she'd stand in a certain way - she'd hunch her shoulders, her chest would become concave, she'd have this nervous body language and she'd become Judy.
"But nothing fitted! We had to fit the dress to match her stoop. I thought, 'She's never going to keep this up - it's too painful' but she did."
None of the costumes in the film are exact replicas off Judy's outfits, partly due to copyright reasons but also because Jany was keen to offer her own interpretation.
She said: "We weren't making a documentary about her.
"I had the same attitude to the costumes that Renee had for Judy, which was understanding the character and creating something she could have worn - but my interpretation of it."
The costume designer was very impressed by the lead actress' knowledge of her role and thinks that made her own job easier.
She said: "She was so on top of her subject and knowledgeable that I couldn't lag behind. But she was so enthusiastic - it was wonderful to design for an actress who really believed in the part."