You know where we stand on the importance of including one great suit in your workwear arsenal, but don’t assume that you’re all set just because you dropped some dough on a decent mid-weight wool number with a double vent. A suit is one of the best – and best-looking – boosts to your work wardrobe, but common tailoring mistakes will wreck your excellent investment faster than you can say “hem it to here.”

To save you from yourself, we got the scoop on common fit errors and how to fix them courtesy of Alan Whitfield, National Director of Tailored Clothing at the venerable Canadian menswear retailer Harry Rosen. You can thank us post-promotion.

Mistake #1: Wrong shoulder shape
The wrong suit shoulder shape can make you look stoop-shouldered (bad) or like an ‘80s boy band member (worse). “Probably the most important thing for people to look for when buying a suit is the shoulder line, because most of the garment’s appeal and personality comes through that,” Whitfield says.

The fix:
Whitfield suggests analyzing your own shoulder shape before you buy to determine whether you’re better suited to a more natural or more structured shoulder.

“If I have a high shoulder, is it better for me to [wear] a more structured shoulder?” asks Whitfield. “If I have more sloped shoulders, is it better to have a more natural shoulder with less padding? Those things will be key for selecting the right garment.” Keep in mind that whatever style of shoulder pad you choose, the pad should end where your actual shoulder ends.

Mistake #2: Shrunken Suit Syndrome
For the past several seasons, the trend in men’s suiting has been increasingly smaller and tighter, but while a little fitted is fine, painted on is not.

“If you look at a garment that’s tailored too close to the body, it wrinkles a lot more, it stresses the fabric and the seams of the garment a lot more, and it doesn’t look as crisp as it could,” Whitfield says.

The fix:
To look professional but still stylish, aim for a fitted silhouette – but don’t cut off your circulation, either. “Good dress trousers should have a bit of a flow,” explains Whitfield. “They should be tailored and close to the body, but also be functional and have some longevity. If you have a really tightly fitted garment, it wears a lot quicker than a garment with a bit more comfort.”

Mistake #3: Wrong sleeve length
If your suit jacket sleeves are so long your fingers barely peek out or your jacket cuffs stretch three inches up your arm, you’ll look like you’re wearing either your dad’s or your little brother’s suit jacket. News flash: neither transmits a confident, professional vibe.

The fix:
Whitfield suggests that suit jacket sleeves be tailored so about a quarter of an inch of shirt cuff is visible. “There’s a level of taste and proportion that needs to be applied,” he emphasizes. “You don’t want look like you’re wearing somebody else’s jacket.”

Mistake #4: Wrong trouser length
Suit trousers look super sloppy if they’re too long, but sock-revealingly short can look pretty silly, too.

The fix:
“The rule used to be that the pant should fall to the back of the heel at the back of the shoe; now, in some cases, the back of the pant doesn’t even touch the back of the shoe,” Whitfield observes. The recommendation? “Something that falls between the ankle and the heel of the shoe – something that has a nice soft gentle break but is still current. A lot of that depends on the style of pant you get – a narrower pant will require a different finished length than a fuller trouser.”