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Get Rid of the Fabric Bump Above a Mock Fly Zipper

Sometimes, no matter how hard you try, there’s an area on a garment you’ve made that just doesn’t look the way you intended. You followed the pattern, made sure all the seam allowances were accurate, but it’s still there. No one would ever notice, but you know it’s there and it bugs you. You’re not alone. After installing a mock fly zipper, I would always get a little “bump” in the fabric just below the waistband.

The following tiny fix solved the problem for me. I know I’m obsessed, but I was much happier after applying my solution.

I’ll walk you through installing a mock fly zipper, to show the bump afterward. Then you’ll see my tiny fix to solve the issue.

Install the mock fly zipper

1. Use tailor’s tacks to indicate the mock fly extension, center-front, and the shape of the stitching for the fly. You may decide to use another method that won’t stain your fabric.

Tailor's tacks used to mock zipper location
2. Use a piece of fusible stay tape, interfacing or a “sew in” stay to keep the underlap area from stretching. Be sure to stabilize any area where a zipper is to be installed.

Tip: I use the 1-inch-wide fusible stay tapes from Sewkeyse; I can use as is or cut it in half to make a 1/2-inch-wide tape as well.

Stabilize the underlap for the zipper
3. Turn the garment over and apply the same stabilization to the center front. Sew the seam together (from above the crotch for pants), to the indication for the bottom of the zipper. Backstitch. Then machine-baste the zipper opening closed. It’s much easier to install this type of zipper without fabric flapping open.

Stabilize the center front

4. Turn the garment back over so that you can press the underlap area flat.

The fusible stay tape…

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Previous: When Armani Makes Pants Next: Reset a Side Zipper in Pants for a Better Fit


  1. user-7035420 | | #1

    Question. At what point are you cutting off the top of the zipper?

  2. User avater
    pamhoward | | #2

    Hi, I wait until I’ve sewn the waistband across the top. This will prevent any chance of the zipper pull coming off. Many years ago, I installed a zipper and cut the excess from the upper end before applying the waistband or waist facing. I zipped it up and the zipper pull kept going off of the zipper... not fun to replace it!

  3. User avater
    [email protected] | | #3

    Thank you so much Pam. I really love the beautifully polished effect without the bump and I will try to incorporate this tip in my future sewing.

    1. User avater
      pamhoward | | #5

      You’re very welcome!

  4. osewviolet | | #4

    What causes the bump in the first place? Does the fabric stretch during the zipper installation?

    1. User avater
      pamhoward | | #6

      Hi, even though you stabilize the fabric, it does still have a tendency to “grow” a little bit there. That little adjustment has always worked for me :-)

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