This has to be, hands-down, one of the most infuriating work issues on the planet. It goes without saying that you’re not going to be best friends will all of your co-workers, but not being buddy-buddy with someone is a far cry from having a colleague who tells lies that affect your performance, your supervisor’s perception of you, or your relationship with a client.

It could be as minor as pretending an email was never received (though, really, in this day and age, that’s hardly a credible story) or as major as telling your boss that you criticized someone’s work and decided to do the project all on your own because you said "it would be better this way.” The he-said, she-said aspect of that example gives me a headache.

But then, if you’re dealing with a lying, manipulative co-worker, you're probably starting to experience more and more annoying moments at the office. Fortunately, there are ways to combat the situation before a lie costs you your reputation (or temper). Muse Career Coach Lea McLeod understands all too well the frustration with lying colleagues, saying that “When people lie to us, it goes against our basic need to be liked and approved of.” Moreover, it can make us wonder, “Does this person take me for an idiot or what? Of course, I really know what’s going on here.”

A lying co-worker needs to be put in his place, but gently. It’s important not to lose your cool and to approach the situation with as much delicacy as you can muster. You’ve been the professional one this long; don’t stop now. Ahead, three steps to navigating this ultra-frustrating work problem.

1. Understand the Situation

McLeod urges you to “stay rooted in facts versus emotion,” which can be difficult when dealing with a conflict like this. She suggests that rather than “focusing on the judgment, (e.g., ‘Becky is such a liar!’), work to get an understanding of the situation.” Try to get a sense of why the person may be doing this, again and again. Is it out of fear, insecurity, or performance anxiety?

Avoid going behind your co-worker’s back and spreading the word of her manipulative ways. Nobody likes a gossip, even if the gossiper is venting a frustration. Lying isn’t OK, obviously, but if the root of the problem is a deep-seated insecurity or total lack of confidence, it’s worth working through it one-on-one.

2. Have an Honest Conversation

Often a simple and informal chat will do the trick. If you decide to approach your colleague about a lie you are sure he’s told, allow him to fess up and come clean. Following that, “you can have a conversation about your expectation that it will never happen again,” says McLeod.

If the fib was attached to an extenuating circumstance, say, a colleague lied about following up with potential candidates because she was afraid to let you know she was feeling overwhelmed and hadn’t gotten to it yet, this opens up a discussion about workload and the need for enhanced communication.

If the truth as you’re sure you know it doesn’t come out, move on to the next step.

3. Provide Proof of the Lie

This part isn’t pretty, but in the event that the co-worker you confront continues to tell bald-faced lies, you’re going to have to bring out the big guns. McLeod recommends leveraging “what evidence you have that illustrates the situation. If there are emails, texts or other documentation, you’ll need to refer to that.”

Of course, if you’re preparing to discuss a loaded situation like this, you should be ready with documentation to back up your story and show that you haven’t just jumped to conclusions about someone’s behavior. McLeod says to try this: “Becky, in an email on Friday at 2 PM, you told me you had spoken with the customer. But the customer called me this morning and indicated you had not spoken.”

Try not to fly off the handle; instead, aim to get to the bottom of the situation. If a colleague's been making up stories behind your back, you have a right to dig into that and find out why the backstabbing's been going on. McLeod says to “stay focused on the facts, and not the judgment of the other person.”

You may not get the answer you’re looking for—or any answer at all, for that matter—but you’ll have put it out there that you know what’s been going on. At least then, the unprofessional co-worker may back off, realizing that his lies are only bound to hurt him in the long run.

Photo of man looking at computer courtesy of Shutterstock.